Issue #237: Skip Git-ignored project files when compressing folders

Manual UI verification (isolated ad-hoc signed Release build, not installed):
- General Settings shows the option and explanation; toggled it on.
- Quick Compress options reflected the enabled preference.
- Add to Archive save options reflected the enabled preference.
- Dismissed the save panel without saving and restored the setting to off.

Automated verification:
- swift test --package-path Modules: 582 tests in 138 suites passed.
- MacPacker Release and MacPacker Store Release Store unsigned builds: passed.
- scripts/check-architectures.sh: 15 bundled Mach-O files checked; all include arm64 and x86_64.
- Empty-selection regression reproduced before the fix; all 5 focused tests pass afterward.
- git diff --check: passed.