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/vitest.config.ts

@@ -1,7 +1,9 @@
 import { defineConfig } from "vitest/config";
 import { resolve } from "path";
+import solid from "vite-plugin-solid";
 
 export default defineConfig({
+  plugins: [solid()],
   test: {
     environment: "jsdom",
   },