Carry alternating CQ on after a contact

Alternating CQ ran off every message the keyer finished, so working a
station that answered started a CQ on the other radio, and Escape --
which stopped it outright -- was the way around that. It now follows
N1MM: only the CQ message carries the alternation to the other radio,
anything else holds it where it is, and so does Escape. The next CQ
picks it up again, which is what the CQ after a logged contact does, so
Ctrl+B is needed once rather than after every contact.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RoGtneMQaz4M9w7Kk49AVD

README.md

@@ -474,9 +474,15 @@ Not there yet: voice keying on the second radio.
 ### Alternating CQ
 
 **Ctrl+B** calls CQ on one radio, and when that message has gone out, moves to
-the other radio and calls there, until Escape or another Ctrl+B. The keyboard,
-the entry window and the SO2R box follow each turn. N1MM calls this dueling CQs
-and puts it on the same key.
+the other radio and calls there, until another Ctrl+B switches it off. The
+keyboard, the entry window and the SO2R box follow each turn. N1MM calls this
+dueling CQs and puts it on the same key.
+
+Only the CQ carries it on to the other radio. Sending anything else — the other
+station's call, the exchange — holds the CQ where it is, and so does Escape, so
+a station that answers can be worked without switching alternating CQ off. The
+next CQ picks it up again, which is what the CQ after a logged contact does.
+N1MM works the same way.
 
 It runs off the keyer saying the message has gone out, not off a guess at how
 long the text takes: `cwdaemon` answers the `<ESC>h` reply request, and a