feat: add app and menu bar icons

[HanminYIN]

Summary

• add a complete macOS AppIcon asset catalog based on the Linx68 display, knob, and keyboard silhouette
• add a monochrome template MenuBarIcon with native 18 px and 36 px representations for light and dark menu bars
• use the custom menu bar asset with the existing SF Symbol retained as a fallback
• include the asset catalog in both project.yml and the tracked Xcode project, with lifecycle tests covering resource loading, size, and template rendering

Validation

• xcodebuild ... test: 14 tests passed
• universal Release build succeeded for arm64 and x86_64
• codesign --verify --deep --strict passed on the built application
• assetutil confirmed app icon renditions from 16 px through 1024 px and menu bar renditions at 18 px / 36 px