feat: YouTube music download system with admin dashboard

Sidecar architecture: edge functions (auth + DB) → youtube-worker container
(youtubei.js for playlist metadata, yt-dlp for audio downloads).

- Edge functions: youtube-playlist, youtube-process, youtube-status (CRUD)
- youtube-worker sidecar: Node.js + yt-dlp, downloads M4A to Supabase Storage
- Admin music page: import playlists, process queue, inline genre editing
- 12 music genres with per-track assignment and import-time defaults
- DB migrations: download_jobs, download_items tables with genre column
- Deploy script and CI workflow for edge functions + sidecar

supabase/functions/deno.json

@@ -0,0 +1,8 @@
+{
+  "imports": {
+    "@supabase/supabase-js": "https://esm.sh/@supabase/supabase-js@2"
+  },
+  "compilerOptions": {
+    "strict": true
+  }
+}