fix(anomalies): skip orphan-event rows in the feed instead of crashing

AnomalyBrowsingService.TryProject fell back to `new SportCode(0)` when an anomaly's
event was missing — but SportCode throws for 0, which would blow up the whole
feed/dashboard for that row. Anomalies have an FK to events so it was dead in
practice, but an orphaned row now degrades gracefully (skipped, like a row with
unparseable evidence). Closes the flagged latent crash.

- TryProject returns false when the event lookup misses; +1 test.

src/Marathon.UI/Services/AnomalyBrowsingService.cs

@@ -137,14 +137,16 @@ public sealed class AnomalyBrowsingService : IAnomalyBrowsingService
 
         var severity = AnomalySeverityRules.FromScore(anomaly.Score);
 
-        events.TryGetValue(anomaly.EventId, out var ev);
+        // Skip orphan anomalies whose event has been pruned — degrade gracefully rather
+        // than throwing on a sentinel SportCode(0). Anomalies have an FK to events so this
+        // is defensive; the feed already drops rows whose evidence won't parse.
+        if (!events.TryGetValue(anomaly.EventId, out var ev) || ev is null)
+            return false;
 
-        var sport = ev?.Sport ?? new SportCode(0);
-        var country = ev?.CountryCode ?? string.Empty;
-        var league = ev?.LeagueId ?? string.Empty;
-        var title = ev is not null
-            ? ev.Title
-            : anomaly.EventId.Value;
+        var sport = ev.Sport;
+        var country = ev.CountryCode;
+        var league = ev.LeagueId;
+        var title = ev.Title;
 
         var preSnap = ToSnapshot(dto.PreSuspension);
         var postSnap = ToSnapshot(dto.PostSuspension);