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/playbooks/new-page.md

@@ -0,0 +1,18 @@
+# Playbook: New H5 Page
+
+Use when: “新增页面”
+
+## Steps
+
+1. Confirm IA tab vs secondary page (`.ai/ui.md`)
+2. Read `.ai/design/design-system.md` + `component-catalog.md` + `design/platform/h5.md`
+3. Reuse catalog components; update catalog if adding a new one
+4. Add route in `apps/user-h5/src/router`
+5. Add `pages/XxxPage.vue` (PascalCase); tokens only (no raw brand hex)
+6. Extract components if file approaches 300–400 lines
+7. Data via `src/api` → `@yuxingu/sdk` only
+8. Use domain words from `.ai/domain.md`
+9. Loading / empty / error states
+10. Compliance copy if report-like
+11. `npm run build:h5`
+12. Review + checklist/feature.md