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.

MediaBrowser.Controller/Session/SessionInfo.cs

@@ -178,6 +178,16 @@ namespace MediaBrowser.Controller.Session
         /// <value>The application version.</value>
         public string ApplicationVersion { get; set; }
 
+        /// <summary>
+        /// Gets or sets the instance ID that owns this session.
+        /// </summary>
+        /// <value>The instance ID.</value>
+        /// <remarks>
+        /// Used for multi-instance deployments to track which Jellyfin instance
+        /// is managing this session's resources (transcoding, network connections, etc.).
+        /// </remarks>
+        public Guid InstanceId { get; set; }
+
         /// <summary>
         /// Gets or sets the session controller.
         /// </summary>