feat(cat): MY_RIG follows the radio that is connected

With one rig, MY_RIG belonged in Operating conditions and nowhere else.
With several, that becomes the wrong place: operating conditions describe
a PLAN — 'on 20 m I use the beam and the 7300' — while the question a
logged QSO asks is which radio was keying.

So each saved radio carries its own MY_RIG, consulted BEFORE the per-band
station. When the two disagree — a second rig borrowed for one evening on
20 m — the one that is transmitting is the true answer.

Left empty it changes nothing at all: the old chain (band default, then
the profile's rig) answers exactly as it did, which is what every
single-radio station will keep doing without touching a setting.

app_radios.go

@@ -43,6 +43,14 @@ type RadioConfig struct {
 	// the CAT panel has always edited, so a saved radio is exactly "what the
 	// settings said the day it was saved".
 	Settings CATSettings `json:"settings"`
+	// MyRig is what goes into MY_RIG on a QSO made with this radio.
+	//
+	// It belongs here rather than in Operating conditions once there is more
+	// than one rig: the operating conditions describe a PLAN — "on 20 m I use
+	// the beam and the 7300" — while this is the fact of which radio is keying.
+	// Left empty, nothing changes: the old chain (band default, then the
+	// profile's rig) answers exactly as it did.
+	MyRig string `json:"my_rig"`
 }
 
 // radioLabel is what the status bar shows when the operator never named one.
@@ -204,3 +212,26 @@ func (a *App) syncActiveRadio(s CATSettings) {
 		}
 	}
 }
+
+// activeRadioMyRig is the MY_RIG of the radio currently connected, or "".
+//
+// Consulted BEFORE the per-band default, and deliberately: the band default is
+// what the operator planned to use on that band, this is which radio is
+// actually on the air. When they disagree — a second rig borrowed for one
+// evening on 20 m — the one that is transmitting is the true answer.
+func (a *App) activeRadioMyRig() string {
+	if a.settings == nil || strings.TrimSpace(a.settingOr(keyRadiosList, "")) == "" {
+		return "" // no list was ever made: nothing to say, nothing changes
+	}
+	list, err := a.GetRadios()
+	if err != nil {
+		return ""
+	}
+	id := a.ActiveRadioID()
+	for _, r := range list {
+		if r.ID == id {
+			return strings.TrimSpace(r.MyRig)
+		}
+	}
+	return ""
+}