perf: batch repository reads, index snapshots, centralize date encoding

- Add IEventRepository/IResultRepository.GetManyAsync to kill N+1 lookups at
  6 sites (backtest, outcome eval, both bet-journal paths, anomaly browsing,
  results selection); guarded by a Received(1).GetManyAsync test.
- Add EventRepository.QueryAsync to push date+sport filtering to SQL (was
  load-whole-range-then-filter); search/sort stay in-memory for Cyrillic order.
- Add AnomalyRepository.CountSinceAsync (unread badge) + ListByDateRangeAsync
  (feed date filter); add Event/Snapshot count methods for the dashboard.
- Add composite indexes IX_Snapshots_EventCode_CapturedAt and
  _EventCode_Source_CapturedAt via a new migration + model snapshot.
- Introduce SqliteDateText as the single source of the O-format date encoding
  shared by Mapping (read/write) and the repositories' range predicates.
- Fix LiveOddsPoller cadence drift (budget sleep against cycle time); make
  DetectAnomalies dedup O(1) per event; add Event.Title to dedup the title join.

Tests adapted to the batched GetManyAsync via a TestFixtures bridge.

tests/Marathon.Application.Tests/UseCases/EvaluateAnomalyOutcomesUseCaseTests.cs

@@ -22,6 +22,14 @@ public sealed class EvaluateAnomalyOutcomesUseCaseTests
     private readonly IEventRepository _events = Substitute.For<IEventRepository>();
     private readonly IResultRepository _results = Substitute.For<IResultRepository>();
 
+    public EvaluateAnomalyOutcomesUseCaseTests()
+    {
+        // Use cases batch event/result loads via GetManyAsync; route those through
+        // the per-id GetAsync stubs each test already configures.
+        TestFixtures.BridgeGetMany(_events);
+        TestFixtures.BridgeGetMany(_results);
+    }
+
     private static readonly TimeSpan MoscowOffset = TimeSpan.FromHours(3);
     private static readonly DateTimeOffset BaseTime =
         new(2026, 5, 10, 18, 0, 0, MoscowOffset);
@@ -287,6 +295,36 @@ public sealed class EvaluateAnomalyOutcomesUseCaseTests
         report.EventTitles[id].Should().Be("Team A vs Team B");
     }
 
+    [Fact]
+    public async Task Should_BatchEventAndResultLoads_InsteadOfPerIdGetAsync()
+    {
+        // Regression guard for the N+1 fix: the use case must resolve events/results
+        // via the batched GetManyAsync, never the per-id GetAsync in a loop. We stub
+        // GetManyAsync directly (overriding the constructor bridge) so DidNotReceive()
+        // on GetAsync is meaningful.
+        var id1 = new EventId("11111111");
+        var id2 = new EventId("22222222");
+
+        _anomalies.ListAsync(Arg.Any<CancellationToken>())
+            .Returns(new[] { MakeAnomaly(id1, 0.55m), MakeAnomaly(id2, 0.55m) }.ToList().AsReadOnly());
+
+        _events.GetManyAsync(Arg.Any<IReadOnlyCollection<EventId>>(), Arg.Any<CancellationToken>())
+            .Returns(new Dictionary<EventId, Event> { [id1] = MakeEvent(id1, 11), [id2] = MakeEvent(id2, 6) });
+        _results.GetManyAsync(Arg.Any<IReadOnlyCollection<EventId>>(), Arg.Any<CancellationToken>())
+            .Returns(new Dictionary<EventId, EventResult>());
+
+        await CreateSut().ExecuteAsync(CancellationToken.None);
+
+        await _events.Received(1)
+            .GetManyAsync(Arg.Any<IReadOnlyCollection<EventId>>(), Arg.Any<CancellationToken>());
+        await _events.DidNotReceive()
+            .GetAsync(Arg.Any<EventId>(), Arg.Any<CancellationToken>());
+        await _results.Received(1)
+            .GetManyAsync(Arg.Any<IReadOnlyCollection<EventId>>(), Arg.Any<CancellationToken>());
+        await _results.DidNotReceive()
+            .GetAsync(Arg.Any<EventId>(), Arg.Any<CancellationToken>());
+    }
+
     [Fact]
     public async Task Should_HandleMissingEvent_By_OmittingFromSportBuckets()
     {