feat(anomaly): IAnomalyDetector seam + steam-move detector

- Introduce IAnomalyDetector; the existing flip detector implements it.
- Extract MatchWinEvidence so every detector writes the identical pre/post
  evidence shape — the UI parser and outcome evaluator handle new kinds with no
  branching (steam moves get hit-rate calibrated for free).
- Add SteamMoveDetector: flags a rapid one-directional implied-probability rise
  over a short CONTINUOUS window (no suspension gap inside it), so it never
  double-flags the same interval as the suspension-flip detector.
- DetectAnomaliesUseCase fans out over both detectors; dedup keys on EventId+Kind
  so flip and steam signals persist independently. Add AnomalyKind.SteamMove +
  SteamMove window/threshold options. 8 detector tests.

src/Marathon.Application/UseCases/DetectAnomaliesUseCase.cs

@@ -59,10 +59,18 @@ public sealed class DetectAnomaliesUseCase
     {
         _logger.LogInformation("DetectAnomaliesUseCase: cycle started");
 
-        var detector = new AnomalyDetector(
-            _options.SuspensionGapSeconds,
-            _options.OddsFlipThreshold,
-            _options.MinSnapshotCount);
+        var detectors = new IAnomalyDetector[]
+        {
+            new AnomalyDetector(
+                _options.SuspensionGapSeconds,
+                _options.OddsFlipThreshold,
+                _options.MinSnapshotCount),
+            new SteamMoveDetector(
+                _options.SteamMoveWindowSeconds,
+                _options.SteamMoveDriftThreshold,
+                _options.MinSnapshotCount,
+                _options.SuspensionGapSeconds),
+        };
 
         var events = await _eventRepo.ListAsync(ct);
         int newAnomalyCount = 0;
@@ -96,7 +104,7 @@ public sealed class DetectAnomaliesUseCase
                 var existingForEvent = existingByEvent.TryGetValue(ev.Id, out var slice)
                     ? slice
                     : new List<Anomaly>();
-                newAnomalyCount += await ProcessEventAsync(detector, ev, snapshots, existingForEvent, ct);
+                newAnomalyCount += await ProcessEventAsync(detectors, ev, snapshots, existingForEvent, ct);
             }
             catch (OperationCanceledException)
             {
@@ -120,13 +128,17 @@ public sealed class DetectAnomaliesUseCase
     // ── Private helpers ───────────────────────────────────────────────────────
 
     private async Task<int> ProcessEventAsync(
-        AnomalyDetector detector,
+        IReadOnlyList<IAnomalyDetector> detectors,
         Event ev,
         IReadOnlyList<OddsSnapshot> snapshots,
         List<Anomaly> existingForEvent,
         CancellationToken ct)
     {
-        var detected = detector.Detect(ev.Id, snapshots);
+        // Fan out over every detector kind; dedup below keys on EventId + Kind so the
+        // flip and steam signals for one event persist independently.
+        var detected = detectors
+            .SelectMany(d => d.Detect(ev.Id, snapshots))
+            .ToList();
 
         if (detected.Count == 0)
             return 0;