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>

DESIGN.md

@@ -0,0 +1,30 @@
+# Design system (Fluksio)
+
+`fluksio` (dashboard SPA + API) and `website` (marketing site) are **separate
+repos** that share one visual design. The full, canonical spec — palette,
+radius, elevation, motion, component map, and shell patterns — lives in the
+parent repo's [`DESIGN-GUIDELINES.md`](../DESIGN-GUIDELINES.md). Read it before
+any UI work.
+
+## Sync rule (read before touching tokens)
+
+The `@theme inline`, `:root`, and `.dark` blocks in `fluksio/frontend/src/index.css`
+and `website/src/index.css` **must be kept byte-identical**, and
+`frontend/src/lib/motion.ts` is duplicated verbatim. Any palette / radius /
+elevation / motion-token change is made in *both* repos in the same change.
+There is intentionally no shared npm package — the duplicated blocks are the
+sync point. Components (`src/components/ui/*`) are copied per repo (the shadcn
+model) and may diverge; only the tokens and motion presets must match.
+
+Both repos share `components.json`: style `new-york`, `cssVariables: true`,
+icon library `lucide`.
+
+Verify with `make design-check` from the workspace root.
+
+## Shell
+
+The authenticated area is a `bg-card` region (`SidebarProvider`) with a floating
+translucent `AppSidebar` (`variant="floating"`, `bg-card/80 backdrop-blur-md`).
+The flow editor floats its chrome over a full-bleed node canvas using the same
+frosted-surface model. See DESIGN-GUIDELINES.md → Shells and → Overlay surfaces
+& content chips.