Adds the shared primitives the planner topbar redesign needs, on the
design-system tokens:
- IconButton — icon-only button (undo/redo), ghost/secondary variants,
requires an accessible label.
- SegmentedControl — generic single-select toggle (color mode
Plain/Elevation/Surface), radiogroup semantics.
- Avatar — colored initial circle for participants, per-user color with
an accent fallback.
Co-located jsdom unit tests for each (roles, aria-checked, onChange,
disabled, color fallback). Extends the dev-only /dev/ui gallery with
sections for all three.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
1bd5f18a33