feat: add subscription service — user auth, Stripe billing, API keys, dashboard

- NextAuth v5 with email+password credentials, JWT sessions
- Registration, login, email verification, password reset flows
- Stripe integration: Free (15/day), Starter ($5/1k/mo), Pro ($20/100k/mo)
- API key management (cb_ prefix) with hash-based validation
- Dashboard with generations history, settings, billing management
- Rate limiting: Redis daily counter (free), DB monthly (paid)
- Generate route auth: Bearer API key + session, anonymous allowed
- Worker userId propagation for generation history
- Pricing section on landing page, auth-aware navbar
- Middleware with route protection, CORS for codeboard.vectry.tech
- Docker env vars for auth, Stripe, email (smtp.migadu.com)

.env.example

@@ -2,7 +2,11 @@ DATABASE_URL=postgresql://codeboard:codeboard@localhost:5432/codeboard
 REDIS_URL=redis://localhost:6379
 OPENAI_API_KEY=
 ANTHROPIC_API_KEY=
-GITHUB_CLIENT_ID=
-GITHUB_CLIENT_SECRET=
-NEXTAUTH_SECRET=
-NEXTAUTH_URL=http://localhost:3000
+LLM_MODEL=
+LLM_BASE_URL=
+AUTH_SECRET=
+STRIPE_SECRET_KEY=
+STRIPE_WEBHOOK_SECRET=
+STRIPE_STARTER_PRICE_ID=
+STRIPE_PRO_PRICE_ID=
+EMAIL_PASSWORD=