feat: Add automatic redirect from auth page to dashboard for logged

[maheshbhatiya73]

• Enhance Auth component to check user authentication state on load
• Add loading spinner while validating existing authentication tokens
• Implement automatic redirect from /auth to /dashboard for authenticated users
• Add debug logging to track authentication flow and token validation
• Fix user data parsing in AuthContext (backend returns user directly, not wrapped)
• Improve error handling and token cleanup for invalid sessions
• Add backend logging for login attempts and token validation debugging

This ensures users who are already logged in are automatically redirected to the dashboard when accessing the auth page, improving UX flow.