feat: stop a QSO recording and play it back on the air

The situation, in the operator's words: working VP2MAA, recording, and he asks
to hear his own signal. So: stop, play, and the recording is still saved with
the QSO.

Stopping FREEZES the take rather than ending it — nothing more is captured,
nothing is discarded, and logging writes the file exactly as before. Playback
reuses the voice keyer's path: same output device, same PTT keying and release
with its generation guard, so a replay cannot be cut short by a stale unkey.

Playing is refused while still recording. The transmitted audio would feed back
into the same take on any rig monitoring its own transmission, and stopping is
one click the operator has already made — it is their statement that the take is
finished, not a hoop.

The elapsed clock freezes with the recording and resumes from where it stopped,
because it now shows the LENGTH OF THE FILE rather than the time since the QSO
began. Only a fresh take returns it to zero.

frontend/wailsjs/go/main/App.d.ts

@@ -753,10 +753,16 @@ export function QSOAudioManualReady():Promise<boolean>;
 
 export function QSOAudioManualStart():Promise<boolean>;
 
+export function QSOAudioPlayOnAir():Promise<void>;
+
 export function QSOAudioResetClock():Promise<boolean>;
 
 export function QSOAudioRestart():Promise<boolean>;
 
+export function QSOAudioResume():Promise<boolean>;
+
+export function QSOAudioStop():Promise<boolean>;
+
 export function QuitApp():Promise<void>;
 
 export function RecomputeAllAwardRefs():Promise<number>;