feat: Kelly criterion stake sizing (domain + MyBets helper)

- Add KellyCalculator (Domain/Betting): pure fractional-Kelly stake from win
  probability, decimal odds, bankroll, and fraction (default quarter-Kelly).
  Returns 0 on non-positive edge; truncates the suggestion down to 2 decimals
  so it never exceeds the computed figure. 19 unit tests.
- MyBets: add a page-local stake helper (bankroll + win-probability inputs) that
  suggests a quarter-Kelly stake from the form's rate, with an Apply button and a
  no-edge message. Win probability is user-supplied, not derived from a signal.
- Localization (en+ru) for the Kelly helper and the export-hub keys (shared resx).

src/Marathon.Domain/Betting/KellyCalculator.cs

@@ -0,0 +1,82 @@
+namespace Marathon.Domain.Betting;
+
+/// <summary>
+/// Pure fractional-Kelly stake sizing for a single back bet at decimal odds.
+/// </summary>
+/// <remarks>
+/// <para>
+/// The Kelly criterion maximises the long-run growth rate of a bankroll by staking
+/// a fraction of it proportional to the edge. For decimal odds <c>o</c> and an
+/// estimated win probability <c>p</c>, the full-Kelly fraction of bankroll is:
+/// </para>
+/// <code>f* = (p·o − 1) / (o − 1)</code>
+/// <para>
+/// When <c>f*</c> is zero or negative there is no positive expected value, and the
+/// suggested stake is <c>0</c> — the calculator never recommends betting into a
+/// negative-EV price. Most disciplined bettors stake a <i>fraction</i> of full
+/// Kelly (e.g. quarter-Kelly, <c>fraction = 0.25</c>) to cut variance and blunt the
+/// impact of probability-estimation error; full Kelly is famously over-aggressive
+/// once <c>p</c> is even slightly wrong.
+/// </para>
+/// <para>
+/// The win probability is an input the bettor supplies — it is intentionally NOT
+/// derived from an anomaly score here, so the calculator stays a pure, reusable
+/// money-management primitive independent of any signal source.
+/// </para>
+/// </remarks>
+public static class KellyCalculator
+{
+    /// <summary>Default Kelly fraction: quarter-Kelly — the conventional variance-safe choice.</summary>
+    public const decimal DefaultFraction = 0.25m;
+
+    /// <summary>
+    /// Full-Kelly fraction of bankroll <c>(p·o − 1)/(o − 1)</c>. May be negative or
+    /// zero, signalling no positive edge. Exposed for callers that want the raw
+    /// figure (e.g. to display the edge) rather than a clamped stake.
+    /// </summary>
+    /// <param name="winProbability">Estimated win probability in the closed interval [0, 1].</param>
+    /// <param name="decimalOdds">Decimal odds, strictly greater than 1.0.</param>
+    public static decimal FullKellyFraction(decimal winProbability, decimal decimalOdds)
+    {
+        if (winProbability is < 0m or > 1m)
+            throw new ArgumentOutOfRangeException(nameof(winProbability), winProbability, "Must be in [0, 1].");
+        if (decimalOdds <= 1m)
+            throw new ArgumentOutOfRangeException(nameof(decimalOdds), decimalOdds, "Decimal odds must be greater than 1.0.");
+
+        return (winProbability * decimalOdds - 1m) / (decimalOdds - 1m);
+    }
+
+    /// <summary>
+    /// Suggested stake using fractional Kelly, rounded down to two decimals so the
+    /// suggestion is never larger than the theoretical figure. Returns <c>0</c> when
+    /// there is no positive edge.
+    /// </summary>
+    /// <param name="winProbability">Estimated win probability in the open interval (0, 1).</param>
+    /// <param name="decimalOdds">Decimal odds, strictly greater than 1.0.</param>
+    /// <param name="bankroll">Total bankroll; must be non-negative.</param>
+    /// <param name="fraction">Kelly fraction in (0, 1]; defaults to <see cref="DefaultFraction"/>.</param>
+    public static decimal SuggestStake(
+        decimal winProbability,
+        decimal decimalOdds,
+        decimal bankroll,
+        decimal fraction = DefaultFraction)
+    {
+        if (winProbability is <= 0m or >= 1m)
+            throw new ArgumentOutOfRangeException(nameof(winProbability), winProbability, "Must be in the open interval (0, 1).");
+        if (bankroll < 0m)
+            throw new ArgumentOutOfRangeException(nameof(bankroll), bankroll, "Must be non-negative.");
+        if (fraction is <= 0m or > 1m)
+            throw new ArgumentOutOfRangeException(nameof(fraction), fraction, "Kelly fraction must be in (0, 1].");
+
+        // FullKellyFraction validates decimalOdds.
+        var full = FullKellyFraction(winProbability, decimalOdds);
+        if (full <= 0m)
+            return 0m;
+
+        var stake = fraction * full * bankroll;
+
+        // Truncate (floor toward zero) to two decimals so a stake suggestion never
+        // exceeds the computed figure — a conservative bias for real-money sizing.
+        return Math.Truncate(stake * 100m) / 100m;
+    }
+}

src/Marathon.UI/Pages/MyBets/Journal.razor

@@ -9,6 +9,7 @@
 
 @page "/my-bets"
 @using Marathon.Application.Betting
+@using Marathon.Domain.Betting
 @implements IDisposable
 @inject IStringLocalizer<SharedResource> L
 @inject IBetJournalService Service
@@ -184,6 +185,50 @@
                                          data-test="journal-add-stake" />
                     </div>
 
+                    <div class="m-journal__form-field m-journal__form-field--wide" data-test="journal-kelly">
+                        <label class="m-journal__form-label">@L["Journal.Kelly.Title"]</label>
+                        <div style="display:flex; flex-wrap:wrap; gap:var(--m-space-3); align-items:flex-end;">
+                            <div style="flex:1 1 150px;">
+                                <span class="m-journal__form-hint">@L["Journal.Kelly.Bankroll"]</span>
+                                <MudNumericField T="decimal?"
+                                                 @bind-Value="_kellyBankroll"
+                                                 Min="0m" Step="50m"
+                                                 Variant="Variant.Outlined"
+                                                 data-test="journal-kelly-bankroll" />
+                            </div>
+                            <div style="flex:1 1 150px;">
+                                <span class="m-journal__form-hint">@L["Journal.Kelly.Probability"]</span>
+                                <MudNumericField T="decimal?"
+                                                 @bind-Value="_kellyProbabilityPercent"
+                                                 Min="0m" Max="100m" Step="1m"
+                                                 Variant="Variant.Outlined"
+                                                 data-test="journal-kelly-prob" />
+                            </div>
+                        </div>
+                        @if (KellySuggestion is { } suggestion)
+                        {
+                            @if (suggestion > 0m)
+                            {
+                                <div style="margin-top:var(--m-space-2); display:flex; align-items:center; gap:var(--m-space-3); flex-wrap:wrap;">
+                                    <span class="m-journal__form-hint" data-test="journal-kelly-suggestion">
+                                        @string.Format(CultureInfo.CurrentCulture, L["Journal.Kelly.Suggestion"].Value, suggestion)
+                                    </span>
+                                    <button type="button" class="m-chip" @onclick="ApplyKellyStake" data-test="journal-kelly-apply">
+                                        @L["Journal.Kelly.Apply"]
+                                    </button>
+                                </div>
+                            }
+                            else
+                            {
+                                <span class="m-journal__form-hint" data-test="journal-kelly-noedge">@L["Journal.Kelly.NoEdge"]</span>
+                            }
+                        }
+                        else
+                        {
+                            <span class="m-journal__form-hint">@L["Journal.Kelly.Hint"]</span>
+                        }
+                    </div>
+
                     <div class="m-journal__form-field m-journal__form-field--wide">
                         <label class="m-journal__form-label">@L["Journal.Field.Notes"]</label>
                         <MudTextField T="string"
@@ -644,6 +689,33 @@
     private string? _formError;
     private Guid? _pendingDeleteId;
     private AddBetForm _form = new();
+
+    // Kelly stake-helper state — page-local (not persisted with the bet). Bankroll
+    // intentionally survives form resets so it carries across successive entries.
+    private decimal? _kellyBankroll;
+    private decimal? _kellyProbabilityPercent;
+
+    /// <summary>
+    /// Quarter-Kelly suggested stake from the entered bankroll + win probability and
+    /// the form's current rate. Null when inputs are incomplete/invalid; 0 when the
+    /// price carries no positive edge.
+    /// </summary>
+    private decimal? KellySuggestion
+    {
+        get
+        {
+            if (_kellyBankroll is not { } bankroll || bankroll <= 0m) return null;
+            if (_kellyProbabilityPercent is not { } pct || pct <= 0m || pct >= 100m) return null;
+            if (_form.Rate <= 1m) return null;
+            return KellyCalculator.SuggestStake(pct / 100m, _form.Rate, bankroll, KellyCalculator.DefaultFraction);
+        }
+    }
+
+    private void ApplyKellyStake()
+    {
+        if (KellySuggestion is { } s && s > 0m)
+            _form.Stake = s;
+    }
     private CancellationTokenSource? _loadCts;
 
     protected override async Task OnInitializedAsync()

src/Marathon.UI/Resources/SharedResource.en.resx

@@ -64,6 +64,7 @@
   <data name="Nav.Anomalies"><value>Anomalies</value></data>
   <data name="Nav.Results"><value>Results</value></data>
   <data name="Nav.Settings"><value>Settings</value></data>
+  <data name="Nav.Export"><value>Export</value></data>
 
   <data name="Home.Kicker"><value>Briefing</value></data>
   <data name="Home.Title"><value>Hunting odds-flip anomalies</value></data>
@@ -262,6 +263,9 @@
   <data name="Export.Submit"><value>Export</value></data>
   <data name="Export.Cancel"><value>Cancel</value></data>
   <data name="Export.Success"><value>Export saved to {0}</value></data>
+  <data name="Export.Hub.Lede"><value>Export captured odds snapshots to an Excel workbook for any date range — no need to open a specific event first.</value></data>
+  <data name="Export.Hub.Action"><value>Configure export</value></data>
+  <data name="Export.Hub.FilenameHint"><value>Saved as Marathon_&lt;from&gt;_to_&lt;to&gt;.xlsx in the configured export directory.</value></data>
   <data name="Export.Error.MissingDates"><value>Pick a start and end date.</value></data>
   <data name="Export.Error.InvalidRange"><value>End date must be on or after the start date.</value></data>
   <data name="Export.Error.Failed"><value>Export failed.</value></data>
@@ -416,6 +420,13 @@
   <data name="Journal.Empty.NotApplicable"><value>—</value></data>
   <data name="Journal.Error.Generic"><value>Failed to save bet — check the event ID and try again.</value></data>
   <data name="Journal.Submitted"><value>Bet recorded.</value></data>
+  <data name="Journal.Kelly.Title"><value>Stake helper (¼-Kelly)</value></data>
+  <data name="Journal.Kelly.Bankroll"><value>Bankroll</value></data>
+  <data name="Journal.Kelly.Probability"><value>Win probability (%)</value></data>
+  <data name="Journal.Kelly.Suggestion"><value>Suggested stake: {0:0.00}</value></data>
+  <data name="Journal.Kelly.Apply"><value>Apply</value></data>
+  <data name="Journal.Kelly.NoEdge"><value>No positive edge at this price.</value></data>
+  <data name="Journal.Kelly.Hint"><value>Enter bankroll + win probability for a ¼-Kelly stake.</value></data>
   <data name="Journal.Resolve.None"><value>No pending bets needed grading.</value></data>
   <data name="Journal.Resolve.Done"><value>Graded {0} pending bet(s).</value></data>
   <data name="Journal.Confirm.Delete"><value>Delete this bet permanently?</value></data>

src/Marathon.UI/Resources/SharedResource.ru.resx

@@ -66,6 +66,7 @@
   <data name="Nav.Anomalies"><value>Аномалии</value></data>
   <data name="Nav.Results"><value>Результаты</value></data>
   <data name="Nav.Settings"><value>Настройки</value></data>
+  <data name="Nav.Export"><value>Экспорт</value></data>
 
   <!-- Home / Dashboard -->
   <data name="Home.Kicker"><value>Сводка</value></data>
@@ -275,6 +276,9 @@
   <data name="Export.Submit"><value>Экспорт</value></data>
   <data name="Export.Cancel"><value>Отмена</value></data>
   <data name="Export.Success"><value>Файл сохранён в {0}</value></data>
+  <data name="Export.Hub.Lede"><value>Экспорт собранных снимков коэффициентов в книгу Excel за любой диапазон дат — без необходимости открывать конкретное событие.</value></data>
+  <data name="Export.Hub.Action"><value>Настроить экспорт</value></data>
+  <data name="Export.Hub.FilenameHint"><value>Сохраняется как Marathon_&lt;от&gt;_to_&lt;до&gt;.xlsx в указанной папке экспорта.</value></data>
   <data name="Export.Error.MissingDates"><value>Выберите даты начала и конца.</value></data>
   <data name="Export.Error.InvalidRange"><value>Дата конца должна быть не раньше даты начала.</value></data>
   <data name="Export.Error.Failed"><value>Экспорт не удался.</value></data>
@@ -429,6 +433,13 @@
   <data name="Journal.Empty.NotApplicable"><value>—</value></data>
   <data name="Journal.Error.Generic"><value>Не удалось сохранить ставку — проверьте ID события и повторите.</value></data>
   <data name="Journal.Submitted"><value>Ставка записана.</value></data>
+  <data name="Journal.Kelly.Title"><value>Калькулятор ставки (¼-Келли)</value></data>
+  <data name="Journal.Kelly.Bankroll"><value>Банкролл</value></data>
+  <data name="Journal.Kelly.Probability"><value>Вероятность выигрыша (%)</value></data>
+  <data name="Journal.Kelly.Suggestion"><value>Рекомендуемая ставка: {0:0.00}</value></data>
+  <data name="Journal.Kelly.Apply"><value>Применить</value></data>
+  <data name="Journal.Kelly.NoEdge"><value>Нет преимущества при этом коэффициенте.</value></data>
+  <data name="Journal.Kelly.Hint"><value>Введите банкролл и вероятность для ставки по ¼-Келли.</value></data>
   <data name="Journal.Resolve.None"><value>Ожидающих ставок к расчёту нет.</value></data>
   <data name="Journal.Resolve.Done"><value>Рассчитано ожидающих: {0}.</value></data>
   <data name="Journal.Confirm.Delete"><value>Удалить эту ставку безвозвратно?</value></data>

tests/Marathon.Domain.Tests/Betting/KellyCalculatorTests.cs

@@ -0,0 +1,133 @@
+using FluentAssertions;
+using Marathon.Domain.Betting;
+
+namespace Marathon.Domain.Tests.Betting;
+
+public sealed class KellyCalculatorTests
+{
+    // ── SuggestStake: edge handling ───────────────────────────────────────────
+
+    [Fact]
+    public void Should_ReturnZeroStake_When_NoPositiveEdge()
+    {
+        // p·o = 0.50 × 1.90 = 0.95 < 1 → negative edge.
+        var stake = KellyCalculator.SuggestStake(
+            winProbability: 0.50m, decimalOdds: 1.90m, bankroll: 1000m);
+
+        stake.Should().Be(0m);
+    }
+
+    [Fact]
+    public void Should_ReturnZeroStake_When_ExactlyBreakeven()
+    {
+        // p·o = 0.50 × 2.00 = 1 → zero edge.
+        var stake = KellyCalculator.SuggestStake(
+            winProbability: 0.50m, decimalOdds: 2.00m, bankroll: 1000m);
+
+        stake.Should().Be(0m);
+    }
+
+    [Fact]
+    public void Should_SizeQuarterKellyStake_When_PositiveEdge()
+    {
+        // full = (0.55×2.10 − 1)/(2.10 − 1) = 0.155/1.10 = 0.140909…
+        // quarter = 0.0352272… × 1000 = 35.2272… → truncated to 35.22.
+        var stake = KellyCalculator.SuggestStake(
+            winProbability: 0.55m, decimalOdds: 2.10m, bankroll: 1000m, fraction: 0.25m);
+
+        stake.Should().Be(35.22m);
+    }
+
+    [Fact]
+    public void Should_UseFullKelly_When_FractionIsOne()
+    {
+        // full = (0.60×2.00 − 1)/(2.00 − 1) = 0.20 → 0.20 × 1000 = 200.
+        var stake = KellyCalculator.SuggestStake(
+            winProbability: 0.60m, decimalOdds: 2.00m, bankroll: 1000m, fraction: 1.0m);
+
+        stake.Should().Be(200m);
+    }
+
+    [Fact]
+    public void Should_ScaleStake_Proportionally_WithBankroll()
+    {
+        var small = KellyCalculator.SuggestStake(0.60m, 2.00m, bankroll: 500m, fraction: 1.0m);
+        var large = KellyCalculator.SuggestStake(0.60m, 2.00m, bankroll: 1000m, fraction: 1.0m);
+
+        small.Should().Be(100m);
+        large.Should().Be(200m);
+    }
+
+    [Fact]
+    public void Should_NeverExceedComputedFigure_When_Truncating()
+    {
+        // Raw quarter-Kelly stake is 35.2272…; the suggestion must floor, not round up.
+        var stake = KellyCalculator.SuggestStake(0.55m, 2.10m, bankroll: 1000m, fraction: 0.25m);
+
+        stake.Should().BeLessThanOrEqualTo(0.25m * KellyCalculator.FullKellyFraction(0.55m, 2.10m) * 1000m);
+    }
+
+    // ── FullKellyFraction ─────────────────────────────────────────────────────
+
+    [Fact]
+    public void FullKellyFraction_Should_ComputeEdgeFraction()
+    {
+        KellyCalculator.FullKellyFraction(0.55m, 2.10m)
+            .Should().BeApproximately(0.140909m, 0.000001m);
+    }
+
+    [Fact]
+    public void FullKellyFraction_Should_BeNegative_When_NoEdge()
+    {
+        KellyCalculator.FullKellyFraction(0.40m, 2.00m).Should().Be(-0.20m);
+    }
+
+    [Fact]
+    public void FullKellyFraction_Should_BeZero_When_Breakeven()
+    {
+        KellyCalculator.FullKellyFraction(0.50m, 2.00m).Should().Be(0m);
+    }
+
+    // ── Guard clauses ─────────────────────────────────────────────────────────
+
+    [Theory]
+    [InlineData(0.0)]
+    [InlineData(1.0)]
+    [InlineData(-0.1)]
+    [InlineData(1.1)]
+    public void SuggestStake_Should_Throw_When_ProbabilityOutOfOpenInterval(double probability)
+    {
+        var act = () => KellyCalculator.SuggestStake((decimal)probability, 2.0m, 1000m);
+
+        act.Should().Throw<ArgumentOutOfRangeException>();
+    }
+
+    [Theory]
+    [InlineData(1.0)]
+    [InlineData(0.5)]
+    public void SuggestStake_Should_Throw_When_OddsNotGreaterThanOne(double odds)
+    {
+        var act = () => KellyCalculator.SuggestStake(0.55m, (decimal)odds, 1000m);
+
+        act.Should().Throw<ArgumentOutOfRangeException>();
+    }
+
+    [Fact]
+    public void SuggestStake_Should_Throw_When_BankrollNegative()
+    {
+        var act = () => KellyCalculator.SuggestStake(0.55m, 2.10m, bankroll: -1m);
+
+        act.Should().Throw<ArgumentOutOfRangeException>();
+    }
+
+    [Theory]
+    [InlineData(0.0)]
+    [InlineData(-0.25)]
+    [InlineData(1.5)]
+    public void SuggestStake_Should_Throw_When_FractionOutOfRange(double fraction)
+    {
+        var act = () => KellyCalculator.SuggestStake(0.55m, 2.10m, 1000m, (decimal)fraction);
+
+        act.Should().Throw<ArgumentOutOfRangeException>();
+    }
+}