feat(ui): shared primitives (Button, Badge, Card, Input) on the tokens

Second step of the visual-redesign (tokens -> primitives -> surfaces):
a small set of shared, token-driven primitives in @trails-cool/ui so
both apps compose from one styled vocabulary instead of hand-rolling
bg-white/text-gray-* per screen.

- @trails-cool/ui now ships React components (Button variants+sizes,
  Badge tones, Card raised/subtle, Input) plus a tiny cn() helper.
  React is a peer dep; package builds with no bundling step.
- Co-located jsdom unit tests (@testing-library/react) assert roles,
  token classes, variant switching, and behavior — run in the existing
  Unit Tests gate, cross-platform, no snapshot baseline needed.
- Tailwind @source directive in both apps' styles.css so the package's
  token utility classes get generated.
- Dev-only /dev/ui gallery route in the planner renders every primitive
  in all states — a zero-dependency stand-in for Storybook. Excluded
  from production builds (NODE_ENV guard in routes.ts).

No app surfaces are refactored yet; adopting the primitives in the
topbar/sidebar/etc. is the surface task groups.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/planner/app/styles.css

@@ -1,6 +1,9 @@
 @import "tailwindcss";
 @import "@trails-cool/ui/theme.css";
 
+/* Scan the shared UI package so its token utility classes are generated. */
+@source "../../../packages/ui/src";
+
 @keyframes slide {
   0% { transform: translateX(-100%); }
   100% { transform: translateX(400%); }