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/patterns/pagination.md

@@ -0,0 +1,22 @@
+# Pattern: Pagination
+
+## Query
+
+`?page=1&page_size=20`
+
+Defaults: page=1, page_size=20, max page_size=100.
+
+## Response data
+
+```json
+{
+  "list": [],
+  "total": 0,
+  "page": 1,
+  "page_size": 20
+}
+```
+
+## SQL
+
+`LIMIT $n OFFSET $m` with bound params. Always return `total` via `COUNT(*)` (or approximate only with ADR).