App for macOS 14+ and notarized

• App is notarized by Apple
• Improve workflow messaging with concise status updates
• Introduces a new mode to use the node tool create-dmg when installed, collapsing the AppleScript DMG build sequence into a single buildDMG stage, while keeping the original AppleScript flow as automatic fallback
• Fix concurrency/sendability warnings in the Xcode project
• Minor UI/default-setting tweaks (fixed main window/sidebar sizing and default output folder on Desktop)
• Xcode project requires Xcode 16+