Introduce Jellyfin.Database.Providers.Postgres project, enabling PostgreSQL as a database backend using Entity Framework Core 10 and Npgsql. Add custom value converters and model builder extensions for PostgreSQL compatibility. Update solution-wide dependencies to Microsoft.EntityFrameworkCore 10.0.3 and Npgsql.EntityFrameworkCore.PostgreSQL 9.0.2 (as a temporary workaround until 10.x is released). Regenerate all relevant NuGet, build, and cache files. Add new and updated binaries, debug symbols, and XML documentation for affected projects. No application source code changes outside of the new provider and supporting infrastructure.
Refactored all C# test files to use explicit namespace declarations and moved all using directives inside the namespace block for consistency. Updated assembly info and cache files to reflect the new build. Adjusted MvcTestingAppManifest.json to use fully qualified assembly names. No functional changes; all updates are related to code style, organization, and project metadata.
wjones