feat: synced lyrics via lrclib.net in a dedicated TUI panel

[gitcoder89431]

Feature

Fetch and display time-synced lyrics (LRC format) in a dedicated panel in the TUI, scrolling automatically with playback position. Uses the free, open lrclib.net API — no auth required.

Why

Synced lyrics are a beloved feature in music players (Spotify, Apple Music, many terminal players). lrclib.net is a community-maintained, free API that returns LRC-format lyrics by artist + title — a perfect fit for tuitube since db.Track already has both fields. Zero cost, no API key, no rate limits for reasonable usage.

API

GET https://lrclib.net/api/get?artist_name={artist}&track_name={title}

Returns syncedLyrics (LRC format) and plainLyrics (fallback). LRC format:

[00:12.34] First line of lyrics
[00:15.00] Second line...

Implementation sketch

1. On track start, fire a background goroutine: fetchLyrics(artist, title) []LrcLine
2. Parse LRC timestamps into []struct{ TimeSec float64; Text string }
3. Add a lyrics panel toggled by a keybind (e.g. l)
4. In nowPlayingTick, find the current LRC line by binary-searching timePos against the timestamp slice
5. Render in a scrollable lipgloss viewport — highlight current line, dim past/future lines
6. Cache lyrics to ~/.cache/tuitube/lyrics/{youtube_id}.lrc to avoid re-fetching

Fallback chain

1. Cached .lrc file
2. lrclib.net synced lyrics
3. lrclib.net plain lyrics (no scrolling, just display)
4. "No lyrics found" empty state

Files likely affected

• New internal/lyrics/lyrics.go package
• internal/screens/ — new lyrics panel or overlay
• internal/app/app.go — keybind + model field for lyrics visibility

Notes

• Japanese/CJK track titles work well with lrclib since it matches by romanized title too
• CleanTitle output from internal/sync/titles.go should be used for the API query, not the raw title