Every PostgreSQL test carries Category=RequiresDocker and the pipeline filters
that category out, so the provider production runs on was never exercised and
two upgrade-path bugs reached it in a row. Nothing covered the whole startup
sequence either - code and schema migrations interleaved the way the migration
service orders them.
- run both database stages through JellyfinMigrationService against a seeded
library and against a fresh install
- take the server from JELLYFIN_TEST_POSTGRES when it is set, else start a
container
- add a pipeline step that runs the PostgreSQL tests on every push and pull
request, with the server inside the step: the kubernetes backend has no
docker daemon, and a service container deadlocks on the workspace volume
