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/startup.json

@@ -9,6 +9,6 @@
     "CacheDir": "C:/ProgramData/jellyfin/cache",
     "LogDir": "C:/ProgramData/jellyfin/log",
     "TempDir": "C:\\Users\\wjones\\AppData\\Local\\Temp\\jellyfin",
-    "WebDir": "C:/ProgramData/jellyfin/wwwroot"
+    "WebDir": "wwwroot"
   }
 }