Refactor PostgreSQL provider: multi-schema & async prep

- Refactor migrations and provider to use multiple PostgreSQL schemas, each matching a legacy SQLite database (activitylog, authentication, displaypreferences, library, users).
- All tables, foreign keys, and indexes are now schema-qualified; Down migration drops tables by schema.
- Provider ensures schemas exist before migrations; entities are mapped to correct schemas in OnModelCreating.
- Add support for max-pool-size, min-pool-size, and multiplexing connection options; update logging accordingly.
- VACUUM ANALYZE now runs per schema during scheduled optimization.
- TruncateAllTablesAsync now truncates tables with schema qualification.
- README updated with schema structure, new options, and multiplexing warnings.
- CacheDecorator now calls async repository methods using .GetAwaiter().GetResult(), with documentation.
- Lays groundwork for full async/await and multiplexing support in the database layer.

Emby.Server.Implementations/Library/KeyframeManager.cs

@@ -29,9 +29,9 @@ public class KeyframeManager : IKeyframeManager
     }
 
     /// <inheritdoc />
-    public IReadOnlyList<KeyframeData> GetKeyframeData(Guid itemId)
+    public async Task<IReadOnlyList<KeyframeData>> GetKeyframeDataAsync(Guid itemId, CancellationToken cancellationToken = default)
     {
-        return _repository.GetKeyframeData(itemId);
+        return await _repository.GetKeyframeDataAsync(itemId, cancellationToken).ConfigureAwait(false);
     }
 
     /// <inheritdoc />