feat(cms): install Payload and serve the admin panel

Payload 3.88 runs inside the Next app against the existing Postgres, in
its own 'payload' schema so no pipeline operation on public — the app
tables, Airflow's metadata, migrate_csv_to_db.py --drop — can reach blog
content.

Its REST API is mounted at /cms-api. /api is the FastAPI proxy's
catch-all, which would swallow every admin call and forward it to the
backend with no error. The mount points live in lib/payloadRoutes.ts so
there is one definition and a test can assert it without importing
Payload: it is ESM-only, next/jest will not transform it, and appending
transformIgnorePatterns cannot un-ignore a package. Forcing it through
transpilePackages would change how the production build bundles Payload
to serve a test, so the live proof that /api still reaches FastAPI stays
where it belongs — the e2e journeys, which call /api/schools.

The package becomes ESM ("type": "module"), which Payload's CLI requires:
richtext-lexical has top-level await and the config cannot be require()d.
Only two files needed renaming, jest.config.cjs and a build script.

The build is verified to succeed with DATABASE_URL and PAYLOAD_SECRET
both unset, which is how CI builds it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017YmbBhr8s7GusjDE12hrZM

nextjs-app/package.json

@@ -2,6 +2,7 @@
   "name": "nextjs-app",
   "version": "0.1.0",
   "private": true,
+  "type": "module",
   "description": "SchoolCompare Next.js Application",
   "scripts": {
     "dev": "next dev",
@@ -14,18 +15,24 @@
   },
   "dependencies": {
     "@floating-ui/react": "^0.27.20",
+    "@payloadcms/db-postgres": "^3.88.0",
+    "@payloadcms/next": "^3.88.0",
+    "@payloadcms/richtext-lexical": "^3.88.0",
     "@types/node": "^25.2.0",
     "@types/react": "^19.2.10",
     "@types/react-dom": "^19.2.3",
     "chart.js": "^4.5.1",
     "eslint": "^9.39.2",
     "eslint-config-next": "^16.1.6",
+    "graphql": "^16.14.2",
     "leaflet": "^1.9.4",
     "next": "^16.1.6",
+    "payload": "^3.88.0",
     "react": "^19.2.4",
     "react-chartjs-2": "^5.3.1",
     "react-dom": "^19.2.4",
     "react-leaflet": "^5.0.0",
+    "sharp": "^0.35.4",
     "typescript": "^5.9.3",
     "zod": "^4.3.6"
   },
@@ -36,7 +43,6 @@
     "@types/jest": "^30.0.0",
     "@types/leaflet": "^1.9.21",
     "jest": "^30.2.0",
-    "jest-environment-jsdom": "^30.2.0",
-    "sharp": "^0.34.5"
+    "jest-environment-jsdom": "^30.2.0"
   }
 }