Add locked Fn dictation and optional output mute

[augiefra]

Summary

Adds an opt-in hands-free dictation flow while preserving the existing hold-to-talk behavior.

• Double-tap fn to keep recording after release.
• Tap fn once more to stop a locked recording.
• Show a lock next to the recording waveform while locked.
• Add optional --mute-output to silence the current output route while recording, then restore its prior mute or volume state.
• Recover cleanly if the event tap is interrupted, or the process receives SIGINT/SIGTERM.

Implementation

The gesture recognition is a small, testable state machine separate from audio capture and UI. The output mute controller uses current AudioObject APIs and is deliberately opt-in so existing users keep today’s audio behavior.

Validation

• swift test — 5 gesture tests passed.
• git diff --check passed.
• No app bundle, signing identity, certificate, downloaded model, dictionary data, icon, or other user-specific files are included.

Coordination

This overlaps with #4 in HotkeyMonitor and part of RecordingOverlay. If #4 lands first, I can rebase this PR and retain only the locked-dictation/audio-specific changes.

Contribution terms

The repository does not currently declare a LICENSE. I am offering these changes to the repository maintainer for review; a project license or contribution policy would make the intended redistribution terms explicit.