Slice 4b frontend half. Jellyfin-touching pages now select a Jellyfin service
instance instead of a machine.
- api/client.ts: Jellyfin-backed calls (counts/libraries/activity/users, media
status/build/stop/force-stop, queryMedia) send jellyfin_service_id.
- hooks/useDashboard, useUsers, useMedia: selector param renamed to
jellyfinServiceId.
- pages/Media + Applications: list jellyfin service instances and persist
jellyfin_service_id in the URL.
- Dashboard (widgets) and Users (default instance) need no selector change.
- Update Applications + Media tests for the new hook/param.
Files/SSH transport keeps machine_id. Verification: frontend lint 0 errors,
build success, 70 tests; backend ruff clean, 222 tests.
Developer
alex