feat: album art in now-playing panel via Kitty/iTerm2 graphics protocol

[gitcoder89431]

Feature

Render the current track's YouTube thumbnail as inline pixel art in the now-playing panel for terminals that support the Kitty graphics protocol or iTerm2 inline image protocol. Gracefully degrade to nothing (or ASCII block art) on unsupported terminals.

Why

Album art is the #1 most-requested feature across terminal music players (rmpc, kew, termusic all highlight it as a major differentiator). It transforms the now-playing panel from a text readout into something that feels like a real music player. tuitube already fetches YouTube metadata — the thumbnail URL is a free byproduct.

Terminal Support

Protocol	Terminals
Kitty graphics protocol	Kitty, WezTerm, Ghostty
iTerm2 inline images	iTerm2, WezTerm
Sixel	mlterm, xterm with sixel, foot
Fallback	All others — render nothing / small ASCII block

Detection: check $TERM, $TERM_PROGRAM, and $KITTY_WINDOW_ID at startup.

Implementation sketch

1. Fetch thumbnail URL from https://i.ytimg.com/vi/{youtube_id}/mqdefault.jpg (160×90, always available)
2. Resize to ~128×128 using golang.org/x/image or github.com/disintegration/imaging
3. Encode and write using Kitty protocol escape sequence (\x1b_Ga=T,...\x1b\\) or iTerm2 (\x1b]1337;File=...)
4. Render in a fixed region of the now-playing panel in Bubble Tea — use a lipgloss box with fixed dimensions so layout doesn't shift when art is absent
5. Cache the last N thumbnails to disk (~/.cache/tuitube/thumbs/) to avoid re-fetching on skip-back

Files likely affected

• internal/screens/nowplaying.go or equivalent now-playing view
• New internal/art/art.go package for protocol detection + rendering

References

• Kitty graphics protocol spec
• rmpc implementation for reference: uses the same Kitty protocol approach