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/examples/good-api.json

@@ -0,0 +1,25 @@
+{
+  "success_example": {
+    "code": 0,
+    "message": "success",
+    "data": {
+      "summary": "简版结论占位",
+      "profile_id": "p_123"
+    }
+  },
+  "error_example": {
+    "code": 30001,
+    "message": "invalid birth date"
+  },
+  "list_example": {
+    "code": 0,
+    "message": "success",
+    "data": {
+      "list": [{ "slug": "mbti", "name": "MBTI" }],
+      "total": 1,
+      "page": 1,
+      "page_size": 20
+    }
+  },
+  "_comment": "Never use {success:true} or {ok:true} as root."
+}