Release v1.8.1

fix: Fix MSIX package identity_name format for v1.8.1

- Change identity_name from invalid 'com.example.demo_flutter' to valid 'DemoFlutter.DemoFlutterApp'
- Resolve MSIX packaging workflow failure due to invalid company name format
- Ensure MSIX identity follows Microsoft's naming requirements (3-50 characters, alphanumeric/period/dash only)
- Update CHANGELOG.md with v1.8.1 fix details
- MSIX identity_name must not use 'com' as company prefix for proper MSIX compliance