chore(rigctld): trace the client exchange

Only PTT transitions were recorded. So when JTDX aborted a transmission
0.86 seconds into a 13.8-second frame, the log showed the abort and the Fake It
frequency restore around it — and not the command that preceded them, which is
the one thing needed to tell whether OpsLog answered something the client could
not accept.

Behind the existing CAT wire-trace switch rather than a new one: this is a line
per poll and would drown an ordinary log, and an operator chasing a rig-control
fault turns that trace on already.

changelog.json

@@ -3,10 +3,12 @@
     "version": "0.25.1",
     "date": "",
     "en": [
-      "Amplifiers: tick the ones sharing a combiner and ON, OFF and OPERATE act on all of them at once. Each keeps its own meters."
+      "Amplifiers: tick the ones sharing a combiner and ON, OFF and OPERATE act on all of them at once. Each keeps its own meters.",
+      "Shared CAT: with the wire trace on, every command a client sends and the answer given are logged."
     ],
     "fr": [
-      "Amplificateurs : coche ceux qui partagent un combiner et ON, OFF et OPERATE agissent sur tous à la fois. Chacun garde ses mesures."
+      "Amplificateurs : coche ceux qui partagent un combiner et ON, OFF et OPERATE agissent sur tous à la fois. Chacun garde ses mesures.",
+      "CAT partagé : avec la trace activée, chaque commande envoyée par un client et la réponse donnée sont journalisées."
     ]
   },
   {