✅ ENHANCED USB CREATOR with MBetterClient Replacement:
- Added optional MBetterClient executable selection (checkbox controlled)
- Replace default MBetterClient with custom version in ISO
- Updates multiple locations in ISO structure for comprehensive replacement
- Validation and file existence checking
- Enhanced confirmation dialog showing all customizations

TECHNICAL DETAILS:
+ MBetterClient selection UI group with browse functionality
+ replace_mbetter_client() method replaces executable in all ISO locations
+ Updated WorkerThread to handle MBetterClient parameter
+ Enhanced validation logic for executable file checking
+ Updated confirmation dialog to show all optional configurations

USER WORKFLOW:
1. Select ISO file (required)
2. Choose USB device (required)
3. Set root password (optional)
4. Add OpenVPN config (optional)
5. Replace MBetterClient executable (optional)
6. Create customized USB with all configurations

This completes the USB creator tool with full customization capabilities.