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.UI/Resources/SharedResource.en.resx

@@ -116,6 +116,9 @@
   <data name="Settings.Scraping.RateLimitRps"><value>Rate limit (RPS)</value></data>
   <data name="Settings.Scraping.RateLimitRps.Hint"><value>Requests per second. 1 is recommended.</value></data>
   <data name="Settings.Scraping.BaseUrl"><value>Base URL</value></data>
+  <data name="Settings.Scraping.BaseUrl.Hint"><value>Must be an absolute http(s) URL, e.g. https://www.marathonbet.by</value></data>
+  <data name="Settings.Scraping.BaseUrl.Invalid"><value>Base URL must be an absolute http(s) address.</value></data>
+  <data name="Settings.Workers.Cron.Invalid"><value>Schedule must be a 5- or 6-field cron expression.</value></data>
   <data name="Settings.Scraping.RequestTimeoutSeconds"><value>Request timeout (sec)</value></data>
   <data name="Settings.Scraping.UsePlaywright"><value>Use Playwright</value></data>
 
@@ -445,6 +448,9 @@
   <data name="Backtest.Section.Equity"><value>Equity curve</value></data>
   <data name="Backtest.Section.Trace"><value>Trade trace</value></data>
   <data name="Backtest.Field.Bankroll"><value>Starting bankroll</value></data>
+  <data name="Backtest.Field.From"><value>From date</value></data>
+  <data name="Backtest.Field.To"><value>To date</value></data>
+  <data name="Backtest.Field.DateRange.Hint"><value>Leave both empty to backtest every graded anomaly.</value></data>
   <data name="Backtest.Field.MinScore"><value>Min anomaly score</value></data>
   <data name="Backtest.Field.MinScore.Hint"><value>Only bet anomalies at or above this confidence.</value></data>
   <data name="Backtest.Field.StakeRule"><value>Staking rule</value></data>