chore: seal Design Vision v1 and monorepo scaffold

Archive the differentiated YuXinGu product docs, AI engineering system,
design contract, and Go/Vue scaffold. Next execution prioritizes Cece-parity
over early innovation (see .ai/product/STRATEGY.md).

Co-authored-by: Cursor <cursoragent@cursor.com>

.ai/design/README.md

@@ -0,0 +1,15 @@
+# AI Design System
+
+Machine-readable **UI/UX/VI contract** for agents generating H5 / Mini Program / Web / App UI.
+
+| File | Purpose |
+|---|---|
+| [design-system.md](design-system.md) | Foundation: tokens, color, type, spacing, motion, voice |
+| [component-catalog.md](component-catalog.md) | Button / Card / Chat / Report / Membership … |
+| [platform/h5.md](platform/h5.md) | Mobile Web implementation limits |
+| [platform/mini-program.md](platform/mini-program.md) | WeChat constraints |
+| [platform/website.md](platform/website.md) | Desktop / SEO / admin |
+| [platform/flutter.md](platform/flutter.md) | Future native |
+
+Runtime tokens: `packages/ui/src/tokens.css`  
+Product chrome / tabs: `../ui.md`