Stream playlist import progress to admin UI

[guidefari]

Problem

When importing a Spotify playlist from /admin/playlists, the UI only shows a queued toast and then goes blind while background enrichment runs.

Current behavior in code:

• Frontend queues POST /music/playlists/import/spotify and shows Import queued
• Backend imports the playlist, then forks background link enrichment with Effect.forkDetach
• No progress or completion state is pushed back to the frontend

Request

Communicate playlist import progress to the frontend in real time via WebSocket or SSE.

Useful progress states could include:

• queued
• import started
• playlist created or updated
• tracks processed: x / y
• background enrichment started
• background enrichment progress: x / y
• completed
• failed

Notes

• I did not find existing WebSocket or SSE plumbing in the app codebase, so this likely needs a fresh realtime path.
• SSE may be enough if this is only server-to-client progress streaming.
• The current import flow lives around:
  • apps/www/src/routes/admin/_components/-PlaylistsTab.tsx
  • apps/vps/src/services/music-entity/playlist-tracks.service.ts

Outcome

The admin playlists screen should show live progress for an in-flight import instead of a one-off queued toast.

[linear-code]

OPS-117