Add Dialog, Tag, Tooltip, Popover, and Alert components; fix Button icon sizes

New primitives completing the ui/ component tier: Dialog (native <dialog>
with focus trapping), Tag (6 colours × 3 variants), Tooltip and Popover
(using @floating-ui/react for positioning), and Alert (5 status variants
with icons, close, and action slot). Reduced Button icon sizes to better
match label text. Added Tag and Alert token layers to tokens.css.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -12,6 +12,7 @@
     "build-storybook": "storybook build"
   },
   "dependencies": {
+    "@floating-ui/react": "^0.27.19",
     "@fontsource-variable/public-sans": "^5.2.7",
     "@tailwindcss/vite": "^4.3.0",
     "clsx": "^2.1.1",