feat: Last.fm scrobbling support

[gitcoder89431]

Feature

Scrobble now-playing and listened tracks to Last.fm so users get listening history, stats, and recommendations from their existing Last.fm account.

Why

Last.fm scrobbling is a low-effort, high-goodwill feature. A significant portion of audiophile terminal users already use Last.fm and will adopt any player that supports it. It requires no UI changes — just a background POST when a track starts and completes.

API

Last.fm has a free, stable API:

• track.updateNowPlaying — call when playback starts
• track.scrobble — call when >50% of track duration has elapsed
• Auth: one-time auth.getMobileSession with username + password MD5 hash, store session key in config

Implementation sketch

1. Add [lastfm] section to future config file (see enhancement: add get_now_playing, remove_from_playlist MCP tools + config file support #38):

   [lastfm]
   api_key    = "..."
   api_secret = "..."
   session_key = "..."  # obtained once via auth flow

2. In nowPlayingTick, when a new track is detected: call updateNowPlaying
3. When timePos / duration > 0.5 on a new track: call scrobble
4. Fire-and-forget goroutine — scrobble errors should never affect playback

Notes

• Requires the config file from enhancement: add get_now_playing, remove_from_playlist MCP tools + config file support #38 to be useful (so the session key persists)
• MusicBrainz IDs could be passed through if available for better Last.fm matching
• The Artist and SongTitle fields in db.Track map directly to Last.fm's artist and track params