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>

components/external-link.tsx

@@ -0,0 +1,25 @@
+import { Href, Link } from 'expo-router';
+import { openBrowserAsync, WebBrowserPresentationStyle } from 'expo-web-browser';
+import { type ComponentProps } from 'react';
+
+type Props = Omit<ComponentProps<typeof Link>, 'href'> & { href: Href & string };
+
+export function ExternalLink({ href, ...rest }: Props) {
+  return (
+    <Link
+      target="_blank"
+      {...rest}
+      href={href}
+      onPress={async (event) => {
+        if (process.env.EXPO_OS !== 'web') {
+          // Prevent the default behavior of linking to the default browser on native.
+          event.preventDefault();
+          // Open the link in an in-app browser.
+          await openBrowserAsync(href, {
+            presentationStyle: WebBrowserPresentationStyle.AUTOMATIC,
+          });
+        }
+      }}
+    />
+  );
+}