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.

tests/Marathon.UI.Tests/Services/AnomalyBrowsingServiceTests.cs

@@ -100,4 +100,20 @@ public sealed class AnomalyBrowsingServiceTests
 
         items.Select(i => i.Score).Should().ContainInOrder(0.80m, 0.60m, 0.40m);
     }
+
+    [Fact]
+    public async Task ListAsync_SkipsOrphanAnomaly_When_EventMissing()
+    {
+        _anomalies
+            .ListByDateRangeAsync(Arg.Any<DateTimeOffset?>(), Arg.Any<DateTimeOffset?>(), Arg.Any<CancellationToken>())
+            .Returns(new[] { Make(AnomalyKind.SuspensionFlip) });
+        // Event pruned → not in the lookup. Must not throw on a SportCode(0) fallback.
+        _events
+            .GetManyAsync(Arg.Any<IReadOnlyCollection<EventId>>(), Arg.Any<CancellationToken>())
+            .Returns(new Dictionary<EventId, Event>());
+
+        var items = await CreateSut().ListAsync(new AnomalyFilter(), CancellationToken.None);
+
+        items.Should().BeEmpty();
+    }
 }