docs(handover): add architecture map and takeover playbook

docs/product-engineering/code-architecture-map.md

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+# Code Architecture Map
+
+This page is the fast handover map for engineers taking over the codebase.
+
+## Repository Structure
+
+- `apps/admin`:
+  Next.js admin panel. Owns auth UI, CMS management screens, and protected workflows.
+- `apps/web`:
+  Next.js public site. Renders CMS-managed content and public-facing routes.
+- `packages/db`:
+  Prisma schema, generated client usage, and data access services.
+- `packages/content`:
+  Domain-level Zod schemas and shared contracts.
+- `packages/crud`:
+  Shared CRUD service pattern (validation, not-found behavior, audit hook contracts).
+- `packages/ui`:
+  Shared UI primitives used by admin/public apps.
+- `packages/i18n`:
+  Shared locale helpers.
+
+## Runtime Boundaries
+
+- Admin app:
+  writes content and settings, enforces RBAC, runs Better Auth route handlers.
+- Public app:
+  reads published content and settings; no public auth coupling.
+- DB package:
+  only data access and business-persistence rules.
+- Content package:
+  only validation and domain typing; no DB or framework runtime coupling.
+
+## Core Feature Modules
+
+- Auth and user guards:
+  `apps/admin/src/lib/auth/server.ts`, `apps/admin/src/app/api/auth/[...all]/route.ts`
+- Access and route permissions:
+  `apps/admin/src/lib/access.ts`, `apps/admin/src/lib/route-guards.ts`
+- Media domain + storage:
+  `packages/db/src/media-foundation.ts`, `apps/admin/src/lib/media/storage.ts`
+- Pages and navigation:
+  `packages/db/src/pages-navigation.ts`, `apps/admin/src/app/pages/*`, `apps/admin/src/app/navigation/*`
+- Commissions and customers:
+  `packages/db/src/commissions.ts`, `apps/admin/src/app/commissions/page.tsx`
+- Announcements and news:
+  `packages/db/src/announcements.ts`, `apps/admin/src/app/announcements/page.tsx`, `apps/admin/src/app/news/page.tsx`
+
+## Extension Rules
+
+- Add/adjust schema first in `packages/content`.
+- Implement persistence in `packages/db`.
+- Wire usage in app route/actions after schema/service are in place.
+- Add tests at service and app-boundary levels before marking TODO items done.