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>

CONTRIBUTING.md

@@ -0,0 +1,31 @@
+# CONTRIBUTING
+
+## AI-first
+
+This project is driven by the **AI Engineering System** under [`.ai/`](.ai/).  
+Agents must load [AGENTS.md](AGENTS.md) and `.ai/*` before coding.
+
+Human product docs (PRD, business) stay in `apps/docs/`.  
+Do **not** treat `apps/docs/standards/` as the source of truth — it only points here for history.
+
+## Local
+
+```bash
+# optional CN Go proxy
+export GOPROXY=https://goproxy.cn,direct
+
+cd apps/api && go mod tidy && go run ./cmd/server
+npm install && npm run dev:h5
+docker compose -f deploy/docker-compose.yml up -d   # postgres
+```
+
+## Git
+
+Trunk-Based: short `feature/*` / `fix/*` into `main`.  
+Commits: Conventional Commits (`feat:`, `fix:`, `docs:`, …).
+
+## PR
+
+- One feature point.
+- Include Review checklist results when AI-assisted.
+- API changes update `proto/openapi.yaml`.