Add Mac App Store distribution target

[austin-smith]

What Changed

• Add dedicated Mac App Store app and widget targets that share the existing Swift sources and assets.
• Add a shared BitDreamAppStore scheme and Sparkle-free App Store Info.plist.
• Compile updater code and controls only when Sparkle is linked, while preserving Sparkle in the direct-download build.
• Configure automatic signing for the App Store target graph and retain Developer ID signing for direct distribution.
• Bump the app and widget marketing version to 2.0.3.
• Document local App Store validation and Xcode Organizer archiving.

Why

The Mac App Store build cannot include Sparkle or its self-update behavior. Separate distribution targets provide an App Store-compliant artifact without changing the existing direct-download release and appcast workflow.

UI Changes

The Mac App Store build omits the Check for Updates command and update settings. The direct-download build retains the existing updater UI.

Validation

• SwiftLint passed.
• Project, plist, and shared-scheme parsing passed.
• macOS tests passed: 223 tests, 0 failures.
• iOS compile check passed.
• Direct macOS Release build passed at 2.0.3 with Sparkle present.
• Mac App Store Release build passed at 2.0.3 with the widget embedded and no Sparkle files, linkage, or Info.plist keys.
• Unsigned Mac App Store Release archive passed.
• Structured autoreview completed with no actionable findings.