feat(icom): live microphone over the network — the last remote brick

The talk button learns the network road the voice keyer already took: when
To-radio is the radio itself, the microphone is captured and re-framed into
the rig's 320-sample packets, the capture callback serving as the clock — the
mic delivers in real time, so no ring and no pacer. Counters and the frame
remainder live on the audio stream, so a talk session spans calls. PTT keys
before and releases after, through the same code as the USB path.

With this, a network Icom is a complete remote station over three UDP ports:
RX audio to the headset, live voice and recorded messages back, CW through
the rig's keyer, CAT for everything else.

app.go

@@ -10729,9 +10729,44 @@ func (a *App) AudioStartTX() error {
 	if strings.TrimSpace(cfg.ToRadio) == "" {
 		return fmt.Errorf(`no "To radio" device set — pick the rig's USB Audio CODEC output in Settings → Audio`)
 	}
+	// Live mic over the radio's own link: the To-radio "device" is the radio.
+	// Fetched before keying so a missing stream refuses cleanly with the PTT
+	// never touched.
+	var netSend func([]byte) error
+	if cfg.ToRadio == audio.NetworkDeviceID {
+		if strings.TrimSpace(cfg.RecordingDevice) == "" {
+			return fmt.Errorf("pick your microphone as the Recording mic in Settings → Audio")
+		}
+		type sender interface {
+			TXAudioSender() (func([]byte) error, error)
+		}
+		err := a.cat.IcomDo(func(ic cat.IcomController) error {
+			p, ok := ic.(sender)
+			if !ok {
+				return fmt.Errorf("this radio cannot take live microphone audio over its link yet")
+			}
+			fn, err := p.TXAudioSender()
+			if err != nil {
+				return err
+			}
+			netSend = fn
+			return nil
+		})
+		if err != nil {
+			return err
+		}
+	}
 	if err := a.pttKey(cfg); err != nil { // key first — no point streaming to a rig that isn't transmitting
 		return err
 	}
+	if netSend != nil {
+		if err := a.audioMgr.StartTXAudioNetwork(cfg.RecordingDevice, netSend); err != nil {
+			a.pttUnkey()
+			return err
+		}
+		applog.Printf("audio: TX start (mic=%q → the radio over the network, ptt=%q)", cfg.RecordingDevice, cfg.PTTMethod)
+		return nil
+	}
 	if err := a.audioMgr.StartTXAudio(cfg.RecordingDevice, cfg.ToRadio); err != nil {
 		a.pttUnkey()
 		return err