feat(backtest): saved strategy presets (strategy editor v1)

Persist named backtest-strategy presets so a staking config (bankroll,
min-score, stake rule, flat/percent/Kelly params) can be saved, listed,
loaded back into the form, and deleted. The per-run date range is not
part of a preset.

- Domain: SavedStrategy record (name trimmed + bounded to 80 chars,
  Create() factory) wrapping the pure BacktestStrategy.
- Persistence: SavedStrategyEntity + config (TEXT decimals, unique
  case-insensitive NOCASE index on Name), repository, mapping, and a
  hand-trimmed AddSavedStrategies migration (additive — only the new
  table). Case-insensitive names mean save-by-name overwrites instead of
  creating near-duplicates.
- Application: SaveStrategyUseCase (upsert by name, keeps Id+CreatedAt) +
  DeleteStrategyUseCase.
- UI: presets panel on the Backtest page (load/save/delete) + service
  methods; fraction<->percent round-trip; en/ru resx.
- Fix: pin Sports.Code as ValueGeneratedNever — it is the bookmaker's
  natural sport id, not an autoincrement surrogate. Corrects long-standing
  model-snapshot drift; the snapshot is regenerated to match the DB.
- 25 tests across all four layers: domain validation, real-SQLite
  round-trip incl. case-insensitive lookup/uniqueness, the upsert use
  case, and the service percent mapping.

src/Marathon.Infrastructure/Persistence/Mapping.cs

@@ -1,3 +1,4 @@
+using Marathon.Domain.Backtesting;
 using Marathon.Domain.Entities;
 using Marathon.Domain.Enums;
 using Marathon.Domain.ValueObjects;
@@ -222,4 +223,33 @@ internal static class Mapping
             NameRu: entity.NameRu,
             NameEn: entity.NameEn,
             Category: entity.Category);
+
+    // ─── SavedStrategy ─────────────────────────────────────────────────────────
+
+    public static SavedStrategyEntity ToEntity(SavedStrategy domain) =>
+        new()
+        {
+            Id = domain.Id.ToString(),
+            Name = domain.Name,
+            StartingBankroll = domain.Strategy.StartingBankroll,
+            MinScore = domain.Strategy.MinScore,
+            StakeRule = (int)domain.Strategy.StakeRule,
+            FlatStake = domain.Strategy.FlatStake,
+            PercentOfBankroll = domain.Strategy.PercentOfBankroll,
+            KellyFraction = domain.Strategy.KellyFraction,
+            CreatedAt = SqliteDateText.Key(domain.CreatedAt),
+        };
+
+    public static SavedStrategy ToDomain(SavedStrategyEntity entity) =>
+        new(
+            Id: Guid.Parse(entity.Id),
+            Name: entity.Name,
+            Strategy: new BacktestStrategy(
+                StartingBankroll: entity.StartingBankroll,
+                MinScore: entity.MinScore,
+                StakeRule: (StakeRule)entity.StakeRule,
+                FlatStake: entity.FlatStake,
+                PercentOfBankroll: entity.PercentOfBankroll,
+                KellyFraction: entity.KellyFraction),
+            CreatedAt: SqliteDateText.Parse(entity.CreatedAt));
 }