feat(auth): Auth.js v5 + Postgres adapter for local smoke test

Wire up NextAuth v5 with @auth/pg-adapter, JWT sessions (edge-friendly),
and a dev Credentials provider for local testing without Google OAuth.

Stack
- next-auth@5.0.0-beta.31, @auth/pg-adapter@1.11.2, @types/pg
- Google OAuth provider via GOOGLE_CLIENT_ID / GOOGLE_CLIENT_SECRET
  (falls back to AUTH_GOOGLE_ID / AUTH_GOOGLE_SECRET)
- Postgres adapter wired to a single pg.Pool in src/lib/db.ts style —
  reads DATABASE_URL with SUPABASE_DB_URL / POSTGRES_URL fallbacks
- JWT session strategy (edge-safe) so the proxy can verify sessions
  without a DB round-trip

Files
- src/auth.config.ts        edge-safe config (Google + authorized cb)
- src/lib/auth.ts           server config (adapter + dev Credentials)
- src/proxy.ts              Next.js 16 proxy (was middleware.ts)
- src/app/api/auth/[...nextauth]/route.ts
                            catch-all handler
- src/app/protected-example/page.tsx
                            demo page that renders auth() session
- src/actions/auth-signin.ts
                            signInWithGoogle, signInWithDev,
                            signOutAction server actions
- src/app/login/LoginClient.tsx
                            added "Sign in with Google" + dev form
- supabase/migrations/204_authjs_tables.sql
                            users / accounts / sessions /
                            verification_token schema (UUID-keyed)
- .env.example              AUTH_SECRET, AUTH_URL, GOOGLE_CLIENT_*,
                            DATABASE_URL, ALLOW_DEV_LOGIN

Removed
- src/middleware.ts         deleted; Next.js 16 only runs one proxy
                            (the new src/proxy.ts is canonical)

Routes
- /login, /admin, /admin/*, /protected-example
                            proxy matcher
- /api/auth/{providers,csrf,signin/<provider>,callback/<provider>,
  session,signout}
                            standard Auth.js endpoints

Local dev
- npm run dev (now runs on port 4000)
- push migration 204 then visit /login
- dev signin works with any non-empty username/password
  (hidden when ALLOW_DEV_LOGIN=false)
- Google signin requires real GOOGLE_CLIENT_ID + redirect URI
  http://localhost:4000/api/auth/callback/google

Verified
- tsc --noEmit clean
- /admin, /admin/orders, /protected-example → 307 to /login
  when unauthenticated
- /api/auth/session returns user after signin
- /protected-example renders session info
- /api/auth/providers returns google + dev-login

Docs
- CLAUDE.md and MEMORY.md updated to reflect the Supabase → Postgres
  + Auth.js v5 pivot

Gradual migration in progress
- src/lib/admin-permissions.ts still uses dev_session / rc_auth_uid;
  the admin shell will show 'Access Denied' for Auth.js-only
  sessions until each page is flipped over
- @supabase/* packages remain in package.json for the same reason
- production deployment (AUTH_URL=https://, __Secure- cookies) is
  out of scope for this pass

package.json

@@ -3,7 +3,7 @@
   "version": "1.0.0",
   "private": true,
   "scripts": {
-    "dev": "node fix-agents.js && next dev --webpack -H 0.0.0.0",
+    "dev": "node fix-agents.js && next dev --webpack -H 0.0.0.0 -p 4000",
     "build": "next build --webpack",
     "start": "next start",
     "lint": "eslint",
@@ -15,6 +15,7 @@
   },
   "dependencies": {
     "@anthropic-ai/sdk": "^0.96.0",
+    "@auth/pg-adapter": "^1.11.2",
     "@clerk/nextjs": "^7.4.2",
     "@google/generative-ai": "^0.24.1",
     "@gsap/react": "^2.1.2",
@@ -30,6 +31,7 @@
     "gsap": "^3.15.0",
     "lucide-react": "^1.17.0",
     "next": "^16.2.6",
+    "next-auth": "^5.0.0-beta.31",
     "next-themes": "^0.4.6",
     "openai": "^6.37.0",
     "papaparse": "^5.5.3",
@@ -50,6 +52,7 @@
     "@tailwindcss/postcss": "^4",
     "@types/node": "^20",
     "@types/papaparse": "^5.5.2",
+    "@types/pg": "^8.20.0",
     "@types/qrcode": "^1.5.6",
     "@types/react": "^19",
     "@types/react-dom": "^19",