Four editable colors (background/foreground/cursor/selection) via a new
ColorPanel modal with built-in presets and live preview. Global default
persists to localStorage and syncs across windows; per-pane overrides ride
on LeafNode.colorOverride in the workspace tree. Titlebar 🎨 button edits
the global theme; per-pane 🎨 chip overrides a single pane. Subsumes the
prior uncommitted softened-foreground tweak into lib/theme.ts.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
