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

.env.example

@@ -0,0 +1,82 @@
+# ============================================================================
+# Route Commerce — Environment variables
+# ============================================================================
+# Copy to `.env.local` and fill in real values for local development.
+# Production: set these in your hosting dashboard (Vercel / Netlify / etc.).
+# ============================================================================
+
+# ── App ─────────────────────────────────────────────────────────────────────
+NEXT_PUBLIC_BASE_URL=http://localhost:4000
+NEXT_PUBLIC_SITE_URL=http://localhost:4000
+
+# ── Database (Postgres, direct — Supabase is being removed) ────────────────
+# Single connection string used by `pg.Pool` in src/lib/auth.ts and the
+# admin-permissions / data-service layer. Format:
+#   postgresql://USER:PASS@HOST:PORT/DBNAME?sslmode=require
+DATABASE_URL=postgresql://postgres:postgres@localhost:5432/route_commerce
+
+# ── Auth.js (NextAuth v5) ───────────────────────────────────────────────────
+# Generate with: npx auth secret
+# Or: openssl rand -base64 32
+AUTH_SECRET=replace-me-with-a-32-byte-base64-string
+
+# Base URL used to build OAuth callback URLs. In dev:
+AUTH_URL=http://localhost:4000
+# In production, set to https://yourdomain.com
+
+# Google OAuth provider.
+# 1. Go to https://console.cloud.google.com/apis/credentials
+# 2. Create an OAuth 2.0 Client ID (type: Web application)
+# 3. Add Authorized redirect URI: http://localhost:3000/api/auth/callback/google
+# 4. Copy client id + client secret below
+GOOGLE_CLIENT_ID=
+GOOGLE_CLIENT_SECRET=
+
+# Auth.js also reads AUTH_GOOGLE_ID / AUTH_GOOGLE_SECRET if you prefer the
+# default NextAuth variable names. The code in src/auth.config.ts falls
+# back to those names if GOOGLE_CLIENT_ID is unset.
+
+# Set to "false" to disable the in-app dev credentials provider even in
+# development. Default: enabled in dev only.
+ALLOW_DEV_LOGIN=true
+
+# ── Supabase (legacy, being removed) ────────────────────────────────────────
+# Still used by the existing admin pages, server actions, and the
+# `getAdminUser` flow. Once the auth migration is complete and the
+# @supabase/* packages are removed, these can go away.
+NEXT_PUBLIC_SUPABASE_URL=
+NEXT_PUBLIC_SUPABASE_ANON_KEY=
+SUPABASE_SERVICE_ROLE_KEY=
+
+# ── Stripe ─────────────────────────────────────────────────────────────────
+STRIPE_SECRET_KEY=
+STRIPE_WEBHOOK_SECRET=
+NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY=
+STRIPE_PRICE_STARTER=
+STRIPE_PRICE_FARM=
+STRIPE_PRICE_ENTERPRISE=
+STRIPE_PRICE_HARVEST_REACH=
+STRIPE_PRICE_WHOLESALE_PORTAL=
+STRIPE_PRICE_WATER_LOG=
+STRIPE_PRICE_AI_TOOLS=
+STRIPE_PRICE_SQUARE_SYNC=
+STRIPE_PRICE_SMS_CAMPAIGNS=
+
+# ── Resend (transactional email) ────────────────────────────────────────────
+RESEND_API_KEY=
+RESEND_WEBHOOK_SECRET=
+
+# ── AI providers ────────────────────────────────────────────────────────────
+OPENAI_API_KEY=
+ANTHROPIC_API_KEY=
+GOOGLE_API_KEY=
+XAI_API_KEY=
+MINIMAX_API_KEY=
+MINIMAX_BASE_URL=https://api.minimax.io/v1
+
+# ── Square (optional) ───────────────────────────────────────────────────────
+SQUARE_APP_SECRET=
+SQUARE_ENVIRONMENT=sandbox
+
+# ── Cron / automation ───────────────────────────────────────────────────────
+CRON_SECRET=replace-me-with-a-random-string