Build desktop app for Intel Macs

[MateoCerquetella]

Summary

• build separate macOS arm64 and x64 DMG/ZIP artifacts on native GitHub runners for stable and nightly releases
• merge both native builds into one architecture-aware Electron update feed before publishing
• make local desktop packaging target the host architecture instead of attempting unreliable native-module cross-builds
• explicitly package the arm64 and x64 Parcel watcher binaries required by the installed host daemon
• document Intel availability and prefer the host-native app in packaged smoke tests

Root cause

The desktop build hard-coded arm64. Simply adding x64 to the same Electron Builder invocation was not reliable because native dependencies such as better-sqlite3 must be prepared for the target Electron ABI on matching hardware. The Parcel watcher platform package was also only a transitive optional dependency, so an Intel app could package without @parcel/watcher-darwin-x64 and crash when starting the host daemon.

Validation

• built the complete x64 desktop app on an Intel Mac (9/9 Turbo tasks passed)
• installed it at /Applications/bb.app and confirmed the server, host daemon, and Parcel watcher child all remain running
• packaged-app smoke test passed against the x64 executable
• Electron executable and Parcel watcher addon verified as Mach-O x86_64
• 22 focused Vitest tests passed
• desktop TypeScript check passed
• Actionlint passed for both changed workflows
• git diff --check passed