feat: turbostarter boilerplate

Production-ready Next.js boilerplate with:
- Runtime env validation (fail-fast on missing vars)
- Feature-gated config (S3, Stripe, email, OAuth)
- Docker + Coolify deployment pipeline
- PostgreSQL + pgvector, MinIO S3, Better Auth
- TypeScript strict mode (no ignoreBuildErrors)
- i18n (en/es), AI modules, billing, monitoring

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/billing/src/providers/lemon-squeezy/index.ts

@@ -0,0 +1,6 @@
+import { setup } from "./client";
+
+setup();
+
+export { checkout, getBillingPortal } from "./checkout";
+export { webhookHandler } from "./webhook";