Handle permission errors when restore replaces existing files

[kzaoaai]

Summary

Fixes a restore crash when an existing destination path cannot be deleted due to filesystem permissions.

Problem

During mackup restore, when a destination already exists and replacement is confirmed, Mackup deletes the existing path before copying from backup.
If deletion raises PermissionError (e.g. protected app-managed paths), restore currently crashes with a traceback.

Changes

• In restore flow (ApplicationProfile.copy_files_from_mackup_folder), catch PermissionError around destination deletion.
• Print the same user-facing permission error message format used for copy failures.
• Skip that item and continue processing remaining files.
• Add regression test covering delete-time PermissionError during restore replacement.

Validation

• Full test suite passes locally.
• New regression test included in tests/test_application.py.