Phase 0: Set up shadcn/ui foundation with OKLCH theme variables,
ThemeProvider, useThemeStore, cn() utility, and components.json.
Phase 1: Replace all raw <button> elements across 9 files (~25 buttons)
with the shadcn Button component wrapper, preserving functional colors
(indigo, blue, emerald tints) via className overrides where needed.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
