refactor: hoist Moscow offset + sport labels into shared helpers (HIGH)

* New Marathon.Domain.ValueObjects.MoscowTime with Offset, Now, and
  EndOfMoscowDay(DateOnly) — replaces ~15 inline TimeSpan.FromHours(3)
  literals across Domain/Application/Infrastructure/UI.
* New Marathon.UI.Services.SportLabels.Resolve(IStringLocalizer, int) —
  replaces 6 near-identical SportLabel switch bodies in EventListShell,
  Events/Detail, Anomalies/AnomalyFeed, Results/ResultsList,
  Results/ResultsLoader, and AnomalyCard. Single source of truth for the
  6/11/22723/43658 sport-code mapping. Pages keep a one-liner wrapper so
  the call sites stay terse.

src/Marathon.UI/Components/ExportDialog.razor

@@ -113,7 +113,7 @@
 
     protected override void OnInitialized()
     {
-        var moscow = DateTimeOffset.UtcNow.ToOffset(TimeSpan.FromHours(3));
+        var moscow = MoscowTime.Now;
         _from = InitialFrom ?? moscow.AddDays(-1).Date;
         _to = InitialTo ?? moscow.AddDays(1).Date;
         _kind = InitialKind;
@@ -140,10 +140,9 @@
         try
         {
             // Use Moscow offset to match domain ScheduledAt invariant.
-            var moscow = TimeSpan.FromHours(3);
             var range = new AppDateRange(
-                new DateTimeOffset(_from.Value.Date, moscow),
-                new DateTimeOffset(_to.Value.Date.AddDays(1).AddSeconds(-1), moscow));
+                new DateTimeOffset(_from.Value.Date, MoscowTime.Offset),
+                MoscowTime.EndOfMoscowDay(DateOnly.FromDateTime(_to.Value.Date)));
 
             var path = await ExportUseCase.ExecuteAsync(range, _kind, CancellationToken.None);
             Dialog.Close(DialogResult.Ok(path));