Style v2 with tailwind-variants/lite

The numbered v2 token scales (text-1…9, rounded-1…6, shadow-1…6)
share a prefix with the color/utility namespaces, and tailwind-merge
(which tailwind-variants runs by default) cannot tell a numeric
text-3 from a color step, so it silently dropped the size whenever a
text-<color> was present. Switch the v2 kit to the merge-free
tailwind-variants/lite entrypoint (added in v3): upgrade
tailwind-variants to ^3.2.2, import tv/VariantProps from
tailwind-variants/lite in the typography primitives, and drop the
per-call twMerge:false.

The legacy v1 kit stays on tailwind-variants (merge intact). Document
the rationale in ui.md and add a packages/ui/src/v2 ESLint guard that
forbids tailwind-variants, tailwind-merge, and clsx.

Signed-off-by: Émile Ré <emile@probo.com>

packages/ui/package.json

@@ -42,7 +42,7 @@
     "rehype-raw": "^7.0.0",
     "remark-gfm": "^4.0.1",
     "tailwind-merge": "^3.4.0",
-    "tailwind-variants": "^1.0.0",
+    "tailwind-variants": "^3.2.2",
     "tailwindcss": "^4.3.1",
     "tw-animate-css": "^1.3.0",
     "zustand": "^5.0.4"