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/forbidden.md

@@ -0,0 +1,37 @@
+# Forbidden — Never
+
+AI obeys NEVER rules strictly.
+
+## Code
+
+- Never use `panic` on request paths.
+- Never ignore errors (`_ = err` on important paths).
+- Never create circular dependencies.
+- Never put SQL in handlers.
+- Never put `gin.Context` in repositories.
+- Never use package-level mutable globals for request state.
+- Never use `SELECT *` in new SQL.
+- Never introduce `any` casually in TypeScript.
+- Never put `fetch` directly in Vue pages.
+
+## API / data
+
+- Never invent response shapes other than `{code,message,data}`.
+- Never use POST for pure read/query.
+- Never skip migration when schema changes.
+- Never hard-delete user PII without explicit task (use soft delete).
+
+## Security / deploy
+
+- Never hardcode passwords, tokens, or secrets.
+- Never commit `.env` or private keys.
+- Never use Docker image tag `latest` in production.
+- Never log full birthday + answers payloads casually.
+
+## Product / process
+
+- Never invent medical efficacy or 吉凶祸福 copy.
+- Never reverse an Accepted ADR without a new ADR + approval.
+- Never modify files outside the current task.
+- Never extend Legacy root HTML unless the task is migration.
+- Never guess requirements — ASK FIRST.