Adopt the shared design token contract

Replace the stock shadcn OKLCH neutral palette (whose teal --primary had no
relation to the brand) with the fluksio token block duplicated verbatim from
the root DESIGN-GUIDELINES.md, add the self-hosted Inter variable face, the
shared lib/motion.ts presets, a DESIGN.md pointer stub and the
no-arbitrary-font-size hook.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.pre-commit-config.yaml

@@ -26,6 +26,14 @@ repos:
         types: [text]
         files: ^frontend/
 
+      # Font sizes come from the Tailwind scale only; see the Typography
+      # section in the root DESIGN-GUIDELINES.md.
+      - id: no-arbitrary-font-size
+        name: no arbitrary text-[…] font sizes
+        entry: 'text-\[[0-9.]+(rem|px|em)\]'
+        language: pygrep
+        files: ^frontend/src/.*\.tsx$
+
       - id: local-ruff-check
         name: ruff check
         entry: uv run ruff check --force-exclude --fix --exit-non-zero-on-fix