Initial commit: Expo app with Better Auth integration

- Complete Expo React Native app setup with TypeScript
- Better Auth authentication system integration
- Secure storage implementation for session tokens
- Authentication flow with login/logout functionality
- API client configuration for backend communication
- Responsive UI components with themed styling
- Expo Router navigation setup
- Development configuration and scripts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

lib/auth/types.ts

@@ -0,0 +1,24 @@
+export interface User {
+  id: string;
+  username: string;
+  email?: string;
+  name?: string;
+  image?: string;
+  createdAt: Date;
+  updatedAt: Date;
+}
+
+export interface Session {
+  user: User;
+  session: {
+    id: string;
+    userId: string;
+    expiresAt: Date;
+    token: string;
+  };
+}
+
+export interface AuthError {
+  message: string;
+  code?: string;
+}