doMove only truncated moves/frames on the first divergence (forkPoint===null).
Subsequent rewind+move appended to the end of the line, corrupting the game
state irrecoverably. Always truncate to the current point before pushing.
Drop the dead forkedMoves state.
- btn-prev/next now use |◄ / ►| (single triangle + bar, was btn-start/end)
- btn-start/end now use |◄◄ / ►►| (double triangle + bar)
- playback-buttons row fills full width with flex:1 on all buttons
- outer two buttons (start/end) slightly smaller via flex:0.65 + 13px SVG
- All 5 playback buttons now use inline SVG triangles/bars — no more
emoji rendering on iOS/Android
- Pause icon in togglePlay() also switches to SVG
- Radio mode toggle becomes a segmented pill control (own row, full width)
- Piece/Board checkboxes each get their own tap-friendly row (min 2.5rem tall)
