Adds docs/roadmap.md outlining the 4-track plan (foundation, surface
aesthetics, organizable panel, theming) and ships the first track.
- Resizable splitter between editor and control surface (drag the seam,
double-click to reset). Width persists in localStorage.
- Custom scrollbars (WebKit pseudo-elements + Firefox scrollbar-color)
applied globally so CodeMirror's .cm-scroller, the right pane and the
piano roll all match the dark theme.
- Header separators between transport / gain / info groups.
- Smooth transitions on buttons, range thumbs and surface borders.
- :focus-visible rings using accent-glow color token.
- Pulse animation on the live status dot.
- New design-system tokens for layout (--right-w, --splitter-w),
timing (--t-fast/base/slow), and panel hierarchy (--panel-hi,
--gutter-hi, --divider, --fg-mute, --accent-glow).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
