Spike S3/S4: ad-hoc signed app, launch at login, input devices without mic permission

[janthoXO]

DESIGN.md section 11 (S3, S4).

S3: does a locally built, ad-hoc signed app (bundle.sh) run without Gatekeeper prompts, and can it register launch at login with SMAppService.mainApp?

• Test on a clean user account and after a reboot.
• Check the "Background item added" notification.
• If it fails: use a LaunchAgent plist in ~/Library/LaunchAgents.

S4: listing and selecting input devices without microphone permission.

• First observation: listing input devices worked on macOS 27 without a prompt.
• Still to check: setting the default input device, on a clean account.
• If it fails: request permission on first run, with an explanation.

[janthoXO]

Findings from testing the Raycast install flow (#19) on macOS 27, on a normal account without a reboot:

• An ad-hoc signed app that a local process copied into ~/Applications has no quarantine xattr, and it launched without a Gatekeeper prompt.
• SMAppService.mainApp.register() worked. sfltool dumpbtm lists the item as [enabled, allowed, notified].
• The Homebrew keg copy (Add Homebrew formula (tap in this repo) #17) also has no quarantine xattr, and it launched through brew services.

Still to check: whether the login item actually starts the app after a reboot or logout, the same checks on a clean account, and S4 (setting the default input device without microphone permission).