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>

.context/turbostarter-framework-context/sections/mobile/billing.md

@@ -0,0 +1,72 @@
+---
+title: Billing
+description: Get started with billing in TurboStarter.
+url: /docs/mobile/billing
+---
+
+# Billing
+
+<Callout title="Fully-featured billing on mobile is coming soon">
+  For now, billing has a limited functionalities on mobile, we're mostly relying on the [web app](/docs/web/billing/overview) to handle billing.
+
+  We are working on a fully-featured mobile billing to help you monetize your mobile app easier. Stay tuned for updates.
+
+  [See roadmap](https://github.com/orgs/turbostarter/projects/1)
+</Callout>
+
+## Fetching customer data
+
+When your user purchased a plan from your landing page or web app, you can easily fetch their data using the [API](/docs/mobile/api/client).
+
+To do so, just call the `/api/billing/customer` endpoint:
+
+```tsx title="customer-screen.tsx"
+import { api } from "~/lib/api";
+
+export default function CustomerScreen() {
+  const { data: customer, isLoading } = useQuery({
+    queryKey: ["customer"],
+    queryFn: handle(api.billing.customer.$get),
+  });
+
+  if (isLoading) return <Text>Loading...</Text>;
+
+  return <Text>{customer?.plan}</Text>;
+}
+```
+
+You may also want to ensure that user is logged in before fetching their billing data to avoid unnecessary API calls.
+
+```tsx title="customer-screen.tsx"
+import { api } from "~/lib/api";
+import { authClient } from "~/lib/auth";
+
+export default function CustomerScreen() {
+  const {
+    data: { user },
+  } = authClient.useSession();
+
+  const { data: customer } = useQuery({
+    queryKey: ["customer"],
+    queryFn: handle(api.billing.customer.$get),
+    enabled: !!user, // [!code highlight]
+  });
+
+  if (!user || !customer) {
+    return null;
+  }
+
+  return (
+    <View>
+      <Text>{user.email}</Text>
+      <Text>{customer.plan}</Text>
+    </View>
+  );
+}
+```
+
+<Callout title="Be cautious!" type="warn">
+  Be mindful when implementing payment-related features in your mobile app. Apple has strict guidelines regarding external payment systems and **may reject your app** if you aggressively redirect users to web-based payment flows. Make sure to review the [App Store Review Guidelines](https://developer.apple.com/app-store/review/guidelines/#payments) carefully and consider implementing native in-app purchases for iOS users to ensure compliance.
+
+  We are currently working on a fully native payments system that will make it easier to comply with Apple's guidelines - stay tuned for updates!
+</Callout>