Add automatic PostgreSQL database creation and migration

- Added Jellyfin.Database.Providers.Postgres project with full EF Core migration support for PostgreSQL.
- Implemented automatic database creation and privilege assignment on startup.
- Generated initial migration and model snapshot for PostgreSQL schema.
- Updated build, test, and dependency files to include PostgreSQL provider and Npgsql packages.
- Added PowerShell script for generating and testing PostgreSQL migrations.
- No changes to application logic outside database provider/migration infrastructure.

tests/Jellyfin.Server.Integration.Tests/obj/project.nuget.cache

@@ -1,6 +1,6 @@
 {
   "version": 2,
-  "dgSpecHash": "HfzlLngu7HE=",
+  "dgSpecHash": "pAHS2jcV+/I=",
   "success": true,
   "projectFilePath": "E:\\Projects\\pgsql-jellyfin\\tests\\Jellyfin.Server.Integration.Tests\\Jellyfin.Server.Integration.Tests.csproj",
   "expectedPackageFiles": [