Add Sparkle automatic updates

[yvette-carlisle]

Summary

• add Sparkle-backed check/install updates in Settings -> About
• publish a signed appcast alongside the macOS release asset
• add local Sparkle update smoke coverage and bump release version to v0.1.3

Validation

• cargo make fmt-swift
• cargo make lint-swift
• cargo make test-macos-native-host-stage
• scripts/smoke/sparkle-update-local.sh --self-check
• scripts/smoke/sparkle-update-local.sh --prepare-only
• full local Sparkle smoke passed before the rebase: 0.1.2 -> 99.0.0 with manual Install and Relaunch confirmation