fix(anomaly): exclude non-directional kinds from grading and backtest

Review follow-up (HIGH): the three detectors fed the same evaluator/backtest, but
SuspensionFreeze is non-directional (favourite unchanged) — grading it as "favourite
won" polluted the hit-rate with the base favourite-win rate, and its high frozen-ness
score always cleared the backtest threshold.

- Add AnomalyKind.IsDirectional() (flip + steam = true, freeze = false).
- AnomalyOutcomeEvaluator returns Unresolved for non-directional kinds (favourites
  still surfaced for display) so they don't distort calibration.
- RunBacktestUseCase skips non-directional anomalies when building candidates.
- Tests for the classification, the evaluator path, and the backtest skip.

src/Marathon.Application/UseCases/RunBacktestUseCase.cs

@@ -3,6 +3,7 @@ using Marathon.Application.Storage;
 using Marathon.Domain.AnomalyDetection;
 using Marathon.Domain.Backtesting;
 using Marathon.Domain.Entities;
+using Marathon.Domain.Enums;
 using Microsoft.Extensions.Logging;
 using DomainEventId = Marathon.Domain.ValueObjects.EventId;
 
@@ -95,6 +96,11 @@ public sealed class RunBacktestUseCase
         {
             ct.ThrowIfCancellationRequested();
 
+            // Only directional kinds are betting signals; SuspensionFreeze (favourite
+            // unchanged) is informational and must not be staked or it would skew ROI.
+            if (!anomaly.Kind.IsDirectional())
+                continue;
+
             // Cannot simulate a bet whose event hasn't been graded yet.
             if (!resultLookup.TryGetValue(anomaly.EventId, out var result))
                 continue;