- Add validateToken() method to userService to check if refresh token is valid
- Automatically redirect to chat if user already has valid session
- Show 'Checking authentication...' loading state during validation
- Prevents unnecessary login if user is already authenticated
- Improves UX by skipping login screen when not needed
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
