Complete multi-instance support: Phases 3–6 & deployment

- Implements Phases 3–6: session isolation, cache coordination, primary election, and file system monitor coordination for Jellyfin with PostgreSQL.
- Adds new database entities (Instance, DistributedLock, FileSystemChange) and EF model configurations.
- Includes SQL migration scripts and EF migration for all required tables, columns, and helper functions.
- Updates Device entity and JellyfinDbContext for multi-instance tracking.
- Integrates new DI services for instance registry, distributed locks, cache coordinator, and primary election.
- Adds publishing profiles (Win/Linux/FrameworkDependent) and automation script for deployment.
- Extensive documentation for architecture, setup, and publishing.
- All changes are backward compatible and build successfully.

Jellyfin.Server/Program.cs

@@ -290,6 +290,11 @@ namespace Jellyfin.Server
             _migrationLogger = StartupLogger.Logger.BeginGroup<JellyfinMigrationService>($"Migration Service");
             var startupConfigurationManager = new ServerConfigurationManager(appPaths, _loggerFactory, new MyXmlSerializer());
             startupConfigurationManager.AddParts([new DatabaseConfigurationFactory()]);
+
+            // Force load database configuration from disk BEFORE initializing DbContext
+            // This ensures database.xml is read from the configured config directory
+            _ = startupConfigurationManager.GetConfiguration("database");
+
             var migrationStartupServiceProvider = new ServiceCollection()
                 .AddLogging(d => d.AddSerilog())
                 .AddJellyfinDbContext(startupConfigurationManager, startupConfig)