feat: add UI primitive library — Button, Card, Input, Badge, Modal, Toast

- Add cn() utility for class merging in lib/utils.ts
- Button: primary/secondary/ghost/danger variants, sm/md/lg sizes, disabled/loading states
- Card: gradient-card background with optional header/footer slots
- Input: text/email/password/number types with label, error, helper text, focus ring
- Badge: default/success/warning/error/info variants
- Modal: Portal-based dialog with focus trap, ESC/backdrop close, animations
- Toast: ToastProvider context with show/dismiss/auto-dismiss and variant support
- Barrel export via index.ts
- 46 unit tests across all primitives
- Configure vitest with vite-plugin-solid for JSX support

web/package.json

@@ -28,6 +28,7 @@
   },
   "devDependencies": {
     "jsdom": "^29.1.1",
+    "vite-plugin-solid": "^2.11.12",
     "vitest": "^4.1.5"
   }
 }