feat(backtest): optional date-range window

- RunBacktestUseCase gains an ExecuteAsync(strategy, DateRange?, ct) overload that
  pushes the date filter to SQL via IAnomalyRepository.ListByDateRangeAsync; the
  existing no-range overload is preserved. +1 use-case test.
- BacktestForm carries optional From/To (Moscow dates) with From<=To validation and
  a ToDateRange() helper; BacktestService threads it through. Backtest page gains two
  clearable date pickers (empty = all anomalies).
- Localization (en+ru) for the backtest date fields and the settings-validation keys
  (shared resx).

src/Marathon.Application/UseCases/RunBacktestUseCase.cs

@@ -1,4 +1,5 @@
 using Marathon.Application.Abstractions;
+using Marathon.Application.Storage;
 using Marathon.Domain.AnomalyDetection;
 using Marathon.Domain.Backtesting;
 using Marathon.Domain.Entities;
@@ -46,17 +47,32 @@ public sealed class RunBacktestUseCase
         _logger = logger ?? throw new ArgumentNullException(nameof(logger));
     }
 
-    public async Task<BacktestResult> ExecuteAsync(
+    /// <summary>Runs the backtest over every graded anomaly (no date filter).</summary>
+    public Task<BacktestResult> ExecuteAsync(
         BacktestStrategy strategy,
         CancellationToken ct = default)
+        => ExecuteAsync(strategy, dateRange: null, ct);
+
+    /// <summary>
+    /// Runs the backtest over anomalies detected within <paramref name="dateRange"/>
+    /// (inclusive); pass <c>null</c> to include every graded anomaly. The date filter
+    /// is pushed to SQL via <see cref="IAnomalyRepository.ListByDateRangeAsync"/>.
+    /// </summary>
+    public async Task<BacktestResult> ExecuteAsync(
+        BacktestStrategy strategy,
+        DateRange? dateRange,
+        CancellationToken ct)
     {
         ArgumentNullException.ThrowIfNull(strategy);
 
         _logger.LogInformation(
-            "RunBacktestUseCase: started — bankroll={Bankroll}, minScore={MinScore}, stakeRule={Rule}",
-            strategy.StartingBankroll, strategy.MinScore, strategy.StakeRule);
+            "RunBacktestUseCase: started — bankroll={Bankroll}, minScore={MinScore}, stakeRule={Rule}, range={Range}",
+            strategy.StartingBankroll, strategy.MinScore, strategy.StakeRule,
+            dateRange is null ? "all" : $"{dateRange.From:O}..{dateRange.To:O}");
 
-        var anomalies = await _anomalies.ListAsync(ct).ConfigureAwait(false);
+        var anomalies = dateRange is null
+            ? await _anomalies.ListAsync(ct).ConfigureAwait(false)
+            : await _anomalies.ListByDateRangeAsync(dateRange.From, dateRange.To, ct).ConfigureAwait(false);
         if (anomalies.Count == 0)
         {
             _logger.LogInformation("RunBacktestUseCase: no anomalies — empty result");