Add configurable image library folder support

[shawonashraf]

Summary

• add a shared AppSettings helper to persist a custom image-library folder path (with default fallback to ~/Documents/Wardrobe/Images)
• update StorageManager so all drag-drop saves and directory imports resolve the active library folder at runtime
• add a new SettingsView so users can choose a custom library folder or revert to the default
• wire app navigation and scene configuration to expose settings in both the sidebar and the macOS Settings window
• update gallery "Open folder" action to open the active configured library directory

Testing

• xcodebuild -project Wardrobe.xcodeproj -scheme Wardrobe -destination 'platform=macOS' build (fails in Linux cloud environment: xcodebuild unavailable)
• which xcodebuild || true; swift --version || true (confirms missing macOS Swift toolchain in this environment)
• xcrun --find xcodebuild || true; uname -a (confirms no Xcode tooling and Linux host)

  

[shawonashraf]

This will close issue #9