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/subscription.ts

@@ -0,0 +1,48 @@
+import { getSubscription } from "@lemonsqueezy/lemonsqueezy.js";
+
+import { HttpStatusCode } from "@turbostarter/shared/constants";
+import { logger } from "@turbostarter/shared/logger";
+import { HttpException } from "@turbostarter/shared/utils";
+
+import { config } from "../../config";
+import { getCustomerByCustomerId, updateCustomer } from "../../lib/customer";
+
+import { toBillingStatus } from "./mappers/to-billing-status";
+
+export const subscriptionStatusChangeHandler = async ({
+  id,
+}: {
+  id: string;
+}) => {
+  const { data } = await getSubscription(id);
+
+  const subscription = data?.data;
+
+  if (!subscription) {
+    throw new HttpException(HttpStatusCode.NOT_FOUND, {
+      code: "billing:error.subscriptionNotFound",
+    });
+  }
+
+  const customer = await getCustomerByCustomerId(
+    subscription.attributes.customer_id.toString(),
+  );
+
+  if (!customer) {
+    throw new HttpException(HttpStatusCode.NOT_FOUND, {
+      code: "billing:error.customerNotFound",
+    });
+  }
+
+  const priceId = subscription.attributes.variant_id.toString();
+  const plan = config.plans.find((p) => p.prices.find((x) => x.id === priceId));
+
+  await updateCustomer(customer.userId, {
+    status: toBillingStatus(subscription.attributes.status),
+    ...(plan && { plan: plan.id }),
+  });
+
+  logger.info(
+    `✅ Subscription status changed for user ${customer.userId} to ${subscription.attributes.status}`,
+  );
+};