Sparkle Auto-Update for macOS Apps

This skill adds Sparkle auto-update support to a native macOS app. Sparkle is the standard open-source framework for macOS app updates outside the Mac App Store.

Overview

The implementation has 4 parts:

1. SPM dependency -- add the Sparkle package to the Xcode project
2. UpdaterManager.swift -- a singleton that wraps SPUStandardUpdaterController
3. Info.plist keys -- SUFeedURL and SUPublicEDKey
4. UI integration -- "Check for Updates" button in settings/menu bar

Step 1: Add Sparkle via SPM

In Xcode: File > Add Package Dependencies > enter: