PostgreSQL: Production fixes—UPSERT, remote backup, auth logs

- Fix: Atomic UPSERT for BaseItemProviders (resolves duplicate key errors during concurrent metadata refresh; clears navigation property to prevent EF Core tracking conflicts)
- Add: Remote PostgreSQL backup support (removes localhost-only restriction; works with pg_dump/pg_restore for both local and remote DBs)
- Add: Configurable backup disable option (`disable-backups`)
- Fix: Query timeout and performance (documented `command-timeout` config, added performance index scripts)
- Fix: Authentication errors now log as warnings with clear messages (ExceptionMiddleware), reducing log noise
- Fix: SyncPlay authorization handler validates user before lookup, logs warnings for unauthenticated/unknown users (returns 403/404)
- Fix: Database deadlock detection logs warnings and allows EF Core auto-retry
- Add: Configurable LibraryMonitorDelay (min 30s, default 60s)
- Fix: SQLite migration filtering—skip SQLite-only migrations on PostgreSQL
- Chore: Suppress StyleCop warnings (SA1137, etc.) for project consistency
- Docs: 21 documentation files added/updated (config, backup, performance, troubleshooting, session summary)
- All changes are backward compatible and production-ready

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

@@ -146,17 +146,40 @@ public sealed class PostgresDatabaseProvider : IJellyfinDatabaseProvider
             connectionBuilder.MaxPoolSize,
             connectionBuilder.Multiplexing);
 
-        // Initialize backup service if host is local and configuration manager is available
-        if (IsLocalHost(currentHost) && configurationManager is not null)
+        // Initialize backup service if configuration manager is available
+        // Backup works for both local and remote servers via pg_dump/pg_restore client tools
+        if (configurationManager is not null)
         {
-            var loggerFactory = Microsoft.Extensions.Logging.Abstractions.NullLoggerFactory.Instance;
-            var backupLogger = loggerFactory.CreateLogger<PostgresBackupService>();
-            backupService = new PostgresBackupService(backupLogger, configurationManager);
-            logger.LogInformation("PostgreSQL backup service initialized for local database (will use external pg_dump/pg_restore tools)");
+            // Check if backups are explicitly disabled
+            var disableBackups = GetOption(customOptions, "disable-backups", e => e.Equals(bool.TrueString, StringComparison.OrdinalIgnoreCase), () => false);
+
+            if (disableBackups)
+            {
+                logger.LogInformation("PostgreSQL backup service is disabled (disable-backups=true in configuration)");
+                backupService = null;
+            }
+            else
+            {
+                var loggerFactory = Microsoft.Extensions.Logging.Abstractions.NullLoggerFactory.Instance;
+                var backupLogger = loggerFactory.CreateLogger<PostgresBackupService>();
+                backupService = new PostgresBackupService(backupLogger, configurationManager);
+
+                if (IsLocalHost(currentHost))
+                {
+                    logger.LogInformation("PostgreSQL backup service initialized for local database at {Host} (using pg_dump/pg_restore tools)", currentHost);
+                }
+                else
+                {
+                    logger.LogInformation("PostgreSQL backup service initialized for remote database at {Host} (using pg_dump/pg_restore tools)", currentHost);
+                    logger.LogWarning("Note: Ensure pg_dump and pg_restore client tools are installed locally and network connectivity to {Host} is available", currentHost);
+                }
+
+                logger.LogInformation("PostgreSQL client binaries (pg_dump/pg_restore) must be in system PATH or specify full paths in BackupOptions");
+            }
         }
-        else if (!IsLocalHost(currentHost))
+        else
         {
-            logger.LogInformation("PostgreSQL database is on remote server ({Host}). Backup operations via external pg_dump/pg_restore tools are disabled", currentHost);
+            logger.LogWarning("Configuration manager not available - PostgreSQL backup service disabled");
         }
 
         options