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/prompts/refactor.md

@@ -0,0 +1,16 @@
+# Prompt: Refactor
+
+Load first: `.ai/constitution.md`, `.ai/architecture.md`, `.ai/coding.md`, `.ai/testing.md`, `.ai/review.md`.
+
+## Process
+
+1. State goal and non-goals. No behavior change unless asked.
+2. Keep layers intact. Improve names, size, and boundaries.
+3. Prefer move/extract over rewrite.
+4. Keep tests green; add tests if extracting scorable logic with none.
+5. Output Review block focusing on Architecture, Readability, Test, Scope.
+
+## Forbidden
+
+- Mixing refactor with feature work in one change set.
+- Breaking public API envelope or URL contracts silently.