fix(icom): switch off a leftover waveform stream at first contact

The 0x27 output flag lives in the RADIO and survives our sessions: a scope
enabled by an older build (or another program) kept flooding every new
session with 700-byte frames — and on the IC-7760 that flood is what kills
the CI-V link. One 'waveform output off' as soon as the rig answers, once per
session; the front-panel display is deliberately untouched.

internal/cat/icomserial.go

@@ -473,6 +473,12 @@ func (b *IcomSerial) ReadState() (RigState, error) {
 		if !b.dspLoaded {
 			b.readDSP()
 			b.dspLoaded = true
+			// Silence any LEFTOVER waveform stream. The 0x27 output flag lives
+			// in the RADIO and survives our sessions: a scope enabled by an older
+			// build (or another program) kept flooding every new session — and on
+			// the IC-7760 that flood is what kills the CI-V link. The display on
+			// the rig's front panel is deliberately untouched.
+			_ = b.execScope("waveform output off (leftover)", civ.SubScopeOn, 0)
 		} else {
 			b.refreshFrontPanel()
 		}