docs(agents): add per-package AGENTS.md for all core-* packages

packages/core-cms/AGENTS.md

@@ -0,0 +1,51 @@
+# AGENTS.md — core-cms
+
+**Composition-only package** that aggregates feature Payload collections and globals into a single Payload config. It does not define its own collections; instead, it imports them from feature packages.
+
+## Responsibilities
+
+- **Compose Payload config** — `buildConfig()` with all collections and globals from features
+- **Type generation** — Output `generated-types.ts` from Payload's TypeScript generator
+- **No collection definitions** — all collections owned by their respective features (`@repo/auth`, `@repo/blog`, etc.)
+- **No business logic** — purely structural assembly
+
+## Allowed imports
+
+- **`@repo/<feature>/cms`** subpath exports only (to get collections/globals)
+  - e.g., `import { articles } from "@repo/blog/cms"`
+  - e.g., `import { users } from "@repo/auth/cms"`
+  - e.g., `import { pages, siteSettings } from "@repo/marketing-pages/cms"`
+
+## Must NOT import
+
+- Any feature's root package or other subpaths (e.g., NOT `@repo/blog/di`, NOT `@repo/blog/entities`)
+- Any app package
+- `@repo/core-shared`, `@repo/core-api`, `@repo/core-trpc`, `@repo/core-ui`
+
+## Public exports
+
+From `package.json`:
+- `.` — the Payload config (default export) + buildConfig re-export
+- `./generated-types` — Payload-generated TypeScript types
+
+Example usage:
+```typescript
+import { buildConfig } from "@repo/core-cms";
+// or
+import type { Config, User, Article } from "@repo/core-cms/generated-types";
+```
+
+## Test conventions
+
+- No unit tests (composition layer)
+- Verify at app boot: `pnpm dev --filter @repo/cms` succeeds and admin UI loads
+- Type generation: `pnpm generate:types` in `apps/cms`
+
+## Structure
+
+```
+src/
+  payload.config.ts          # imports feature /cms exports, calls buildConfig()
+  generated-types.ts         # auto-generated by Payload
+  index.ts                   # re-exports config
+```