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>

proto/openapi.yaml

@@ -0,0 +1,37 @@
+openapi: 3.0.3
+info:
+  title: YuXinGu API
+  version: 0.1.0
+  description: 愈心谷 HTTP API（脚手架）
+servers:
+  - url: http://127.0.0.1:8080
+paths:
+  /api/v1/healthz:
+    get:
+      summary: Liveness
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Envelope'
+  /api/v1/ping:
+    get:
+      summary: Ping
+      responses:
+        '200':
+          description: OK
+components:
+  schemas:
+    Envelope:
+      type: object
+      properties:
+        code:
+          type: integer
+          example: 0
+        message:
+          type: string
+          example: success
+        data:
+          type: object