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/auth/overview.md

@@ -0,0 +1,40 @@
+---
+title: Overview
+description: Get started with authentication.
+url: /docs/mobile/auth/overview
+---
+
+# Overview
+
+TurboStarter uses [Better Auth](https://better-auth.com) to handle authentication. It's a secure, production-ready authentication solution that integrates seamlessly with many frameworks and provides enterprise-grade security out of the box.
+
+<Callout title="Why Better Auth?">
+  One of the core principles of TurboStarter is to do things **as simple as possible**, and to make everything **as performant as possible**.
+
+  Better Auth provides an excellent developer experience with minimal configuration required, while maintaining enterprise-grade security standards. Its framework-agnostic approach and focus on performance makes it the perfect choice for TurboStarter.
+
+  Recently, Better Auth [announced](https://www.better-auth.com/blog/authjs-joins-better-auth) an incorporation of [Auth.js (27k+ stars on Github)](https://authjs.dev/), making it even more powerful and flexible.
+</Callout>
+
+![Better Auth](/images/docs/better-auth.png)
+
+You can read more about Better Auth in the [official documentation](https://better-auth.com/docs).
+
+TurboStarter supports multiple authentication methods:
+
+* **Password** - the traditional email/password method
+* **Magic Link** - magic links with [deep linking](https://docs.expo.dev/linking/overview)
+* **Anonymous** - allowing users to proceed anonymously
+* **OAuth** - OAuth social providers ([Apple](https://www.better-auth.com/docs/authentication/apple), [Google](https://www.better-auth.com/docs/authentication/google) and [Github](https://www.better-auth.com/docs/authentication/github) preconfigured)
+* **Native Apple authentication** - ["Sign in with Apple"](/docs/mobile/auth/oauth/apple) for iOS
+* **Native Google authentication** - ["Sign in with Google"](/docs/mobile/auth/oauth/google) for Android
+
+As well as common applications flows, with ready-to-use views and components:
+
+* **Sign in** - sign in with email/password or OAuth providers
+* **Sign up** - sign up with email/password or OAuth providers
+* **Sign out** - sign out
+* **Password recovery** - forgot and reset password
+* **Email verification** - verify email
+
+You can construct your auth flow like LEGO bricks - plug in needed parts and customize them to your needs.