feat(icom): the ATU can be taken out of line

TUNE (1C 01 02) started a cycle; nothing sent the 0 that puts the tuner back
through. An ATU chip beside SPLIT now toggles it, and the tuner state is read
on the slow front-panel beat so the radio's own TUNER button stays in sync.

app.go

@@ -14533,6 +14533,14 @@ func (a *App) IcomSetSplit(on bool) error {
 	return a.cat.IcomDo(func(ic cat.IcomController) error { return ic.SetIcomSplit(on) })
 }
 
+// IcomSetATU puts the internal tuner in or out of line.
+func (a *App) IcomSetATU(on bool) error {
+	if a.cat == nil {
+		return fmt.Errorf("cat not initialized")
+	}
+	return a.cat.IcomDo(func(ic cat.IcomController) error { return ic.SetATU(on) })
+}
+
 // IcomSetSplitOffset turns split on with a chosen TX offset (Hz) — the
 // console's +1/+5/+10 kHz buttons.
 func (a *App) IcomSetSplitOffset(hz int64) error {