fix(icom): fold the 7760's stereo RX stream down to the mono it plays as

The rig keeps sending two-channel LPCM after rxcodec asks for one — 1280-byte
payloads, 320 stereo frames per 20 ms tick, right channel all zeros in the
capture. Played as mono that interleaving is half-speed metallic garble. A
stereo-sized packet is folded to its left channel; a 640-byte mono packet from
a rig that honours the request passes through untouched.

app.go

@@ -15573,6 +15573,20 @@ func (a *App) reloadCAT() {
 					if err != nil {
 						return
 					}
+					// The IC-7760 streams TWO-channel LPCM whatever the conninfo
+					// asks for (rxcodec 0x02 was requested, 1280-byte payloads
+					// kept arriving — 320 stereo frames per 20 ms tick, right
+					// channel all zeros). Played as mono that is half-speed
+					// metallic garble. A stereo-sized packet is folded to its
+					// left channel; a 640-byte mono packet (a rig that honours
+					// the request) passes through untouched.
+					if len(pcm) == 1280 {
+						mono := make([]byte, len(pcm)/2)
+						for i := 0; i+3 < len(pcm); i += 4 {
+							mono[i/2], mono[i/2+1] = pcm[i], pcm[i+1]
+						}
+						pcm = mono
+					}
 					a.audioMgr.PushMonitorAudio(pcm)
 					// And to the QSO recorder, which has no device to capture from
 					// on this backend. It drops the samples unless a recording is