Fix the mini player's crushed layout, square its artwork, add a mini …

[perminder-klair]

…button

The mini window's cover sleeve was a , which stretches to fill its row: it took 240x120 of a 420-wide row, leaving the metadata column 24px wide. The title rendered one letter per line and the artist text overflowed to 373px inside a 102px row. Swap it for a hugging explicitly-sized art, the way the LIVE stage's sleeve does, and give the metadata column min-width 0.

The three metadata lines had no wrap/overflow rules, so the artist line still wrapped past the row once it had width. They elide now. That cost the title's bold weight and the artist/album ink-vs-muted split: both came from , and the SDK rejects wrap/overflow on a span paragraph because inline spans always word-wrap and the paragraph reserves the wrapped height. In a window fixed at 168pt, a deterministic single line beats the styling — size carries the hierarchy instead.

The drag strip padded only its leading edge. Per the both-edges rule in CLAUDE.md the window-control cluster trails on Windows, so EXPAND needed the {chrome_trailing} spacer too; it is zero on macOS.

Also, per review:

• Artwork is , not — avatar renders a disc, and a record sleeve is square. Same has_cover / initials-tile fallback as the stage.
• Sleeve padding and corner radius come down on both players (stage 12 -> 5, mini 6 -> 3, both radius -> sm) so the frame reads as a hairline.
• New masthead button toggles mini mode, using a new app:mini picture-in-picture glyph; the builtin icon set has nothing for it.
• The back panel's gear becomes panel-right: settings read as preferences-only, but the panel is SHOWS/TIMELINE/BOOTH/REQUEST as well, and it opens as a right-hand column.

The masthead button makes the "shortcut is the only way into mini mode" comment in main.zig and the README's mini bullet stale; both updated.

native test passes; both windows verified against the running app.