feat(anomaly): suspension-freeze detector

- Add SuspensionFreezeDetector via the IAnomalyDetector seam: a suspension gap with
  the favourite unchanged and a negligible (< threshold) price move — the mirror of
  the flip. Score = how completely the line froze. Reuses MatchWinEvidence so UI +
  evaluator handle it unchanged. 6 tests.
- Add AnomalyKind.SuspensionFreeze + localized card/detail label, SuspensionFreezeThreshold
  option, and fan it into DetectAnomaliesUseCase.

src/Marathon.Application/UseCases/DetectAnomaliesUseCase.cs

@@ -70,6 +70,10 @@ public sealed class DetectAnomaliesUseCase
                 _options.SteamMoveDriftThreshold,
                 _options.MinSnapshotCount,
                 _options.SuspensionGapSeconds),
+            new SuspensionFreezeDetector(
+                _options.SuspensionGapSeconds,
+                _options.SuspensionFreezeThreshold,
+                _options.MinSnapshotCount),
         };
 
         var events = await _eventRepo.ListAsync(ct);