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/bugfix.md

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+# Prompt: Bugfix
+
+Load first: `.ai/constitution.md`, `.ai/coding.md`, `.ai/security.md`, `.ai/review.md`.
+
+## Process
+
+1. Reproduce or state the failure mode clearly.
+2. Find root cause (file + function). Prefer evidence over guess.
+3. Fix the smallest correct change.
+4. Add a regression test when the bug is in scoring, auth, or payment.
+5. Verify build/health.
+6. Output Review block (at least Architecture, Security, Test, Scope).
+
+## Forbidden
+
+- Drive-by refactors unrelated to the bug.
+- Swallowing errors to “make it pass”.

.ai/prompts/new-feature.md

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+# Prompt: New Feature
+
+Load first: `.ai/constitution.md`, `.ai/architecture.md`, `.ai/coding.md`, `.ai/api.md`, `.ai/review.md`, `.ai/definition-of-done.md`.
+
+## Process
+
+1. Restate the feature in one sentence and list files you will touch.
+2. Follow feature flow: API → Service → Repository → Migration → SDK/types → UI → Test → Docs.
+3. Implement the smallest vertical slice that works end-to-end.
+4. Run builds/tests for touched sides.
+5. Output `.ai/review.md` Review block.
+6. Confirm Definition of Done.
+
+## Forbidden
+
+- Inventing APIs not in the task / OpenAPI.
+- Editing legacy root HTML unless migration is the task.
+- Shipping UI-only unlock/payment without server checks.

.ai/prompts/refactor.md

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+# 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.