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.

src/Marathon.UI/Services/AnomalyBrowsingService.cs

@@ -28,10 +28,12 @@ public sealed class AnomalyBrowsingService : IAnomalyBrowsingService
     {
         ArgumentNullException.ThrowIfNull(filter);
 
-        var all = await _anomalies.ListAsync(ct).ConfigureAwait(false);
+        // Date filter pushed to SQL; severity needs the parsed score and sport needs
+        // the event join, so those two stay in memory over the smaller returned set.
+        var all = await _anomalies.ListByDateRangeAsync(filter.From, filter.To, ct).ConfigureAwait(false);
         if (all.Count == 0) return Array.Empty<AnomalyListItem>();
 
-        // Resolve event metadata in one pass — distinct EventIds only.
+        // Resolve event metadata in one batched pass — distinct EventIds only.
         var eventLookup = await BuildEventLookupAsync(all, ct).ConfigureAwait(false);
 
         var items = new List<AnomalyListItem>(all.Count);
@@ -44,7 +46,7 @@ public sealed class AnomalyBrowsingService : IAnomalyBrowsingService
             }
         }
 
-        // Apply filters in-memory (small list, UI page).
+        // Remaining filters in-memory (page-sized set).
         IEnumerable<AnomalyListItem> filtered = items;
 
         if (filter.MinSeverity is { } minSeverity)
@@ -57,16 +59,6 @@ public sealed class AnomalyBrowsingService : IAnomalyBrowsingService
             filtered = filtered.Where(i => sports.Contains(i.Sport.Value));
         }
 
-        if (filter.From is { } from)
-        {
-            filtered = filtered.Where(i => i.DetectedAt >= from);
-        }
-
-        if (filter.To is { } to)
-        {
-            filtered = filtered.Where(i => i.DetectedAt <= to);
-        }
-
         return filtered
             .OrderByDescending(static i => i.DetectedAt)
             .ToList();
@@ -88,16 +80,9 @@ public sealed class AnomalyBrowsingService : IAnomalyBrowsingService
         return new AnomalyDetailVm(item, pre, post);
     }
 
-    public async Task<int> GetUnreadCountAsync(DateTimeOffset since, CancellationToken ct)
-    {
-        var all = await _anomalies.ListAsync(ct).ConfigureAwait(false);
-        var count = 0;
-        foreach (var anomaly in all)
-        {
-            if (anomaly.DetectedAt > since) count++;
-        }
-        return count;
-    }
+    public Task<int> GetUnreadCountAsync(DateTimeOffset since, CancellationToken ct)
+        // Server-side COUNT(*) — no longer materialises the table to count.
+        => _anomalies.CountSinceAsync(since, ct);
 
     public async Task<IReadOnlyList<int>> ListKnownSportCodesAsync(CancellationToken ct)
     {
@@ -125,14 +110,8 @@ public sealed class AnomalyBrowsingService : IAnomalyBrowsingService
             .Distinct()
             .ToList();
 
-        var dict = new Dictionary<DomainEventId, Event>(distinct.Count);
-        foreach (var eid in distinct)
-        {
-            ct.ThrowIfCancellationRequested();
-            var ev = await _events.GetAsync(eid, ct).ConfigureAwait(false);
-            if (ev is not null) dict[eid] = ev;
-        }
-        return dict;
+        // Single batched query instead of one GetAsync per distinct event (N+1).
+        return await _events.GetManyAsync(distinct, ct).ConfigureAwait(false);
     }
 
     private static bool TryProject(
@@ -151,7 +130,7 @@ public sealed class AnomalyBrowsingService : IAnomalyBrowsingService
         var country = ev?.CountryCode ?? string.Empty;
         var league = ev?.LeagueId ?? string.Empty;
         var title = ev is not null
-            ? $"{ev.Side1Name} vs {ev.Side2Name}"
+            ? ev.Title
             : anomaly.EventId.Value;
 
         var preSnap = ToSnapshot(dto.PreSuspension);