fix: auto-detect accessibility permission changes without restart

[jatinkrmalik]

Problem

After reinstalling VocaMac (which resets ad-hoc signing permissions), granting Accessibility permission in System Settings was not reflected in the app until the user either:

• Restarted the app, or
• Clicked "Recheck Permissions" in Settings

Microphone permission worked instantly (callback-based API), but Accessibility and Input Monitoring use AXIsProcessTrustedWithOptions and CGEvent.tapCreate respectively — neither has a callback or notification mechanism.

Solution

Add a lightweight permission polling timer that checks all permissions every 3 seconds until they're all granted.

How it works

• Starts automatically on app launch if any permission is missing
• Starts on demand when the user clicks a permission request button (which opens System Settings)
• Polls every 3 seconds — calls checkPermissions() to refresh all three permission states
• Auto-starts the hotkey listener when Accessibility + Input Monitoring are both granted mid-session (so the user doesn't need to restart)
• Stops itself once all permissions are granted — no wasted CPU cycles during normal operation

Changes (AppState.swift)

• Added permissionPollTimer property
• Added startPermissionPolling() — creates a 3-second repeating timer, guarded against duplicate starts and skipped if all permissions are already granted
• Added stopPermissionPolling() — invalidates and nils the timer
• Added allPermissionsGranted computed property for clean stop condition
• Replaced one-shot DispatchQueue.main.asyncAfter(deadline: .now() + 2.0) delayed rechecks in requestAccessibilityPermission() and requestInputMonitoringPermission() with startPermissionPolling()
• Added startPermissionPolling() call in performStartup() after initial permission check

Testing

All 62 tests pass (swift test). Manually verified:

• Grant Accessibility in System Settings → popover updates within ~3 seconds
• Grant Input Monitoring → same behavior
• Polling stops automatically once all permissions are granted
• Hotkey listener auto-starts after permissions are granted (no restart needed)