Postgres perf, path migration, and shutdown race fixes

- Major query performance boost: replaced correlated subqueries with DistinctBy() in BaseItemRepository, added episode deduplication index, and increased default command timeout to 120s.
- Fixed LibraryMonitor shutdown race: added disposal checks and exception handling in FileRefresher to prevent ObjectDisposedException.
- Added PowerShell and SQL utilities for fixing Linux paths in config files and database; new scripts for WebDir and path migration.
- Auto-fix for WebDir in startup.json on load; new helper scripts and docs.
- Added automated weekly DB performance monitoring scripts and reporting.
- Expanded documentation and README for all fixes, scripts, and migration steps.
- Updated SQL scripts for index creation and diagnostics; improved output handling.
- Updated db-config defaults and added new diagnostic/report files.

src/Jellyfin.Database/Jellyfin.Database.Providers.Postgres/Migrations/20260227000000_AddSupplementaryIndexes.cs

@@ -61,6 +61,14 @@ namespace Jellyfin.Database.Providers.Postgres.Migrations
                     END IF;
                 END $$;
             ");
+
+            // 6. Index for episode deduplication by PresentationUniqueKey
+            // Use case: Group and deduplicate episodes (used in GetItems queries)
+            migrationBuilder.Sql(@"
+                CREATE INDEX CONCURRENTLY IF NOT EXISTS idx_baseitems_presentationuniquekey_episodes
+                ON library.""BaseItems"" (""PresentationUniqueKey"", ""TopParentId"", ""IsVirtualItem"")
+                WHERE ""Type"" = 'MediaBrowser.Controller.Entities.TV.Episode' AND ""PresentationUniqueKey"" IS NOT NULL;
+            ");
         }
 
         /// <inheritdoc />
@@ -72,6 +80,7 @@ namespace Jellyfin.Database.Providers.Postgres.Migrations
             migrationBuilder.Sql(@"DROP INDEX CONCURRENTLY IF EXISTS library.idx_baseitems_datecreated_filtered;");
             migrationBuilder.Sql(@"DROP INDEX CONCURRENTLY IF EXISTS library.idx_itemvaluesmap_itemvalueid_itemid;");
             migrationBuilder.Sql(@"DROP INDEX CONCURRENTLY IF EXISTS activitylog.idx_activitylogs_userid_datecreated;");
+            migrationBuilder.Sql(@"DROP INDEX CONCURRENTLY IF EXISTS library.idx_baseitems_presentationuniquekey_episodes;");
         }
     }
 }

src/Jellyfin.Database/Jellyfin.Database.Providers.Postgres/PostgresDatabaseProvider.cs

@@ -124,7 +124,7 @@ public sealed class PostgresDatabaseProvider : IJellyfinDatabaseProvider
             Username = GetOption(customOptions, "username", e => e, () => "jellyfin")!,
             Password = GetOption(customOptions, "password", e => e, () => string.Empty)!,
             Pooling = GetOption(customOptions, "pooling", e => e.Equals(bool.TrueString, StringComparison.OrdinalIgnoreCase), () => true),
-            CommandTimeout = GetOption(customOptions, "command-timeout", int.Parse, () => 30),
+            CommandTimeout = GetOption(customOptions, "command-timeout", int.Parse, () => 120),
             Timeout = GetOption(customOptions, "connection-timeout", int.Parse, () => 15),
             Multiplexing = GetOption(customOptions, "multiplexing", e => e.Equals(bool.TrueString, StringComparison.OrdinalIgnoreCase), () => false),
             MaxPoolSize = GetOption(customOptions, "max-pool-size", int.Parse, () => 100),