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.

docs/README.md

@@ -260,6 +260,9 @@ tail -f /var/log/jellyfin/log_*.txt
 
 ### 🗄️ PostgreSQL Setup & Migration
 - **[QUICKSTART_POSTGRESQL.md](./docs/QUICKSTART_POSTGRESQL.md)** - Quick PostgreSQL setup
+- **[MULTI_INSTANCE_QUICKSTART.md](./docs/MULTI_INSTANCE_QUICKSTART.md)** - **Quick start for multi-instance deployment** (NEW)
+- **[MULTI_INSTANCE_SUPPORT_PLAN.md](./docs/MULTI_INSTANCE_SUPPORT_PLAN.md)** - **Multi-instance deployment architecture** (NEW)
+- **[MULTI_INSTANCE_SUPPORT_SUMMARY.md](./docs/MULTI_INSTANCE_SUPPORT_SUMMARY.md)** - **Multi-instance implementation status** (NEW)
 - [POSTGRESQL_MIGRATION_COMPLETE.md](./docs/POSTGRESQL_MIGRATION_COMPLETE.md) - Migration guide
 - [POSTGRESQL_TROUBLESHOOTING.md](./docs/POSTGRESQL_TROUBLESHOOTING.md) - Troubleshooting guide
 - [MERGE_MIGRATIONS_GUIDE.md](./docs/MERGE_MIGRATIONS_GUIDE.md) - Merge pending migrations