Add core UI primitives in web/src/ui

Button, IconButton, Tag, Chip, TextInput, Segmented, Toggle, Checkbox,
Slider, Card and ListRow, styled with CSS Modules over the design tokens.
Every interactive primitive keeps a hit area of at least 44 px; visually
smaller controls draw their face inside a larger hit box.

Vitest now injects CSS Modules into jsdom (css: true) so tests assert the
sizes the stylesheets declare, alongside roles, aria states and keyboard
behaviour (Segmented arrow keys, Toggle Space/Enter, Chip "Remove X").

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/vite.config.ts

@@ -14,6 +14,9 @@ export default defineConfig({
   },
   test: {
     environment: 'jsdom',
+    // Inject CSS Modules into jsdom so tests can assert the sizes the
+    // stylesheets actually declare (for example 44 px hit areas).
+    css: true,
     setupFiles: ['./src/test/setup.ts'],
   },
 })