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.

src/Jellyfin.MediaEncoding.Hls/Cache/CacheDecorator.cs

@@ -46,7 +46,14 @@ public class CacheDecorator : IKeyframeExtractor
     /// <inheritdoc />
     public bool TryExtractKeyframes(Guid itemId, string filePath, [NotNullWhen(true)] out KeyframeData? keyframeData)
     {
-        keyframeData = _keyframeRepository.GetKeyframeData(itemId).FirstOrDefault();
+        // Note: This method is synchronous by interface design, but repository is async.
+        // Using GetAwaiter().GetResult() here is acceptable as this is called during media scanning
+        // which is not performance-critical. Consider making IKeyframeExtractor async in future.
+        keyframeData = _keyframeRepository.GetKeyframeDataAsync(itemId, CancellationToken.None)
+            .GetAwaiter()
+            .GetResult()
+            .FirstOrDefault();
+
         if (keyframeData is null)
         {
             if (!_keyframeExtractor.TryExtractKeyframes(itemId, filePath, out var result))
@@ -57,7 +64,9 @@ public class CacheDecorator : IKeyframeExtractor
 
             _logger.LogDebug("Successfully extracted keyframes using {ExtractorName}", _keyframeExtractorName);
             keyframeData = result;
-            _keyframeRepository.SaveKeyframeDataAsync(itemId, keyframeData, CancellationToken.None).GetAwaiter().GetResult();
+            _keyframeRepository.SaveKeyframeDataAsync(itemId, keyframeData, CancellationToken.None)
+                .GetAwaiter()
+                .GetResult();
         }
 
         return true;