feat(omnirig): say which of its two CW bits means CW on this rig

Reported on an IC-7610 shared through OmniRig: clicking a CW spot put
the radio in CW-R every time, and the only way out was to edit the
OmniRig rig file by hand.

OmniRig's model has two CW modes, PM_CW_U and PM_CW_L, and nothing in it
says which one an .ini calls plain CW. Icom rig files disagree with each
other — on some PM_CW_U is CI-V mode 0x03 (CW), on others 0x07 (CW-R) —
so asking for "CW" is a question with two right answers and OpsLog was
only ever giving one of them.

Settings ▸ CAT ▸ OmniRig now carries the answer for THIS rig, and it is
pushed to a radio that is already connected rather than waiting for a
reconnect: which bit a mode maps to is not worth dropping the link, and
with it WSJT-X's rigctl session. Same shape as the Yaesu RTTY sideband,
for the same reason.

Nothing changes for anyone whose rig file already agrees with us.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

internal/cat/cat.go

@@ -1145,6 +1145,23 @@ func (m *Manager) YaesuDo(fn func(YaesuController) error) error {
 	})
 }
 
+// OmniRigController is the handful of OmniRig preferences that can be changed
+// without dropping the rig link.
+type OmniRigController interface {
+	SetCWLower(bool) // which of OmniRig's two CW bits means plain CW
+}
+
+// OmniRigDo dispatches an OmniRig preference onto the CAT goroutine.
+func (m *Manager) OmniRigDo(fn func(OmniRigController) error) error {
+	return m.exec(func(b Backend) error {
+		oc, ok := b.(OmniRigController)
+		if !ok {
+			return fmt.Errorf("active CAT backend is not OmniRig")
+		}
+		return fn(oc)
+	})
+}
+
 // KenwoodController is the Kenwood/Elecraft CW-over-CAT capability (the KY keyer),
 // so a K3 can key CW through its single CAT link instead of a second COM port.
 type KenwoodController interface {