fix(ci): Resolve Windows CI workflow failures

Fixed issues:
- Removed unused 'app' variable from main.py (QMessageBox doesn't need QApplication)
- Added PySide6 installation to all jobs that need it
- Fixed pyflakes command to list files instead of using wildcards
- Simplified type-check to avoid complex inline scripts
- Added shell: pwsh to all Python commands for Windows compatibility
- Fixed syntax check to use os.walk() with Windows paths

Jobs fixed:
- syntax-check: Added PySide6, fixed Windows path commands
- lint-check: Listed specific files instead of core/*.py
- import-check: Added PySide6 installation
- type-check: Simplified script execution
- config-validation: Added PySide6 installation

This resolves CI errors:
- ModuleNotFoundError: No module named PySide6
- TypeError: compile() arg 1 must be a string, bytes or AST object
- Invalid argument errors with pyflakes on Windows
- Local variable 'app' is assigned to but never used

Author: Ian-bug

main.py

@@ -33,7 +33,6 @@ def check_dependencies() -> bool:
             f"pip install {' '.join(missing)}"
         )
         try:
-            app = QApplication(sys.argv)
             QMessageBox.critical(None, "Dependency Error", error_msg)
         except Exception:
             print(error_msg)