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/constitution.md

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+# Project Constitution — 愈心谷
+
+最高原则。与本文件冲突时，以本文件为准。
+
+## Absolute Laws
+
+1. Architecture never broken. Layers: UI → API → Service → Repository → Database. No skipping.
+2. Readability > Cleverness.
+3. Deterministic > Magic.
+4. Simple > Complex.
+5. Explicit > Implicit.
+6. No hidden global state.
+7. Every module independently testable.
+8. Every feature deployable.
+9. Every API documented (OpenAPI or apps/docs).
+10. Every database change versioned (migration required).
+
+## Product Laws (YuXinGu)
+
+1. Never invent medical efficacy claims.
+2. Never use fortune-telling / 吉凶祸福 wording.
+3. Birthday and profile data are sensitive — minimize, authorize, allow delete.
+4. Billing and unlock decisions happen on the server, never trust the client alone.
+5. New product code lives in `apps/` and `packages/` only. Legacy root HTML is read-only unless the task is explicit migration.
+
+## AI Laws
+
+1. Obey `.ai/ai-contract.md` every session.
+2. Load constitution → architecture → domain before writing code.
+3. Never invent APIs/DB/domain words; never reverse Accepted ADRs silently.
+4. Never modify files outside the current task scope.
+5. Prefer patterns + examples + playbooks over prompts.
+6. Prefer small diffs. One feature per change set.
+7. Think → architecture check → code → commands → review → DoD.