Move a playlist from YouTube to Spotify.

1. Copy .env.example to .env and fill in the values:
   • YOUTUBE_API_KEY — from the Google Cloud console (YouTube Data API v3)
   • SPOTIFY_CLIENT_ID / SPOTIFY_CLIENT_SECRET — from the Spotify developer dashboard
2. In the Spotify app settings, add http://127.0.0.1:4321/api/auth/callback (and your production origin's equivalent) to the redirect URIs. Spotify no longer accepts localhost — use the IP form, and open the dev site at http://127.0.0.1:4321 so the derived redirect URI matches.
3. pnpm install && pnpm dev

The conversion is orchestrated by the client in three steps, so each request stays small and the UI can show real progress:

1. GET /api/youtube/playlist?url=... — resolves a playlist URL/ID to its title and tracks
2. POST /api/spotify/search — called once per track, returns the best Spotify match (titles are cleaned of "(Official Video)"-style noise first)
3. POST /api/spotify/playlist — creates the playlist from the matched URIs

Auth endpoints: /api/auth/login, /api/auth/callback, /api/auth/logout, /api/auth/status.

src/
├── components/
│   └── Converter.svelte      # the whole UI (Svelte island)
├── lib/
│   ├── client/
│   │   └── converter.svelte.ts  # client-side conversion state machine
│   ├── youtube.ts    # YouTube Data API client (server-only)
│   ├── spotify.ts    # Spotify OAuth + Web API client (server-only)
│   ├── session.ts    # token cookies + transparent refresh
│   └── match.ts      # title cleaning / search-query building
├── pages/
│   ├── api/          # server endpoints (see above)
│   └── index.astro
└── types.ts          # shared types