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/push-notifications.md

@@ -0,0 +1,13 @@
+---
+title: Push notifications
+description: Engage your users with personalized notifications.
+url: /docs/mobile/push-notifications
+---
+
+# Push notifications
+
+<Callout title="Push notifications are coming soon" type="info">
+  We are working on push notifications to help you engage your users. Stay tuned for updates.
+
+  [See roadmap](https://github.com/orgs/turbostarter/projects/1)
+</Callout>