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.

internal/rigctld/rigctld.go

@@ -32,6 +32,7 @@ package rigctld
 import (
 	"bufio"
 	"fmt"
+	"hamlog/internal/cat"
 	"net"
 	"strconv"
 	"strings"
@@ -244,7 +245,18 @@ func (s *Server) serve(c net.Conn) {
 			s.log("rigctld: client %s disconnected", c.RemoteAddr())
 			return
 		}
-		resp, quit := s.handle(strings.TrimSpace(line))
+		req := strings.TrimSpace(line)
+		resp, quit := s.handle(req)
+		// The whole exchange, when tracing is on.
+		//
+		// Only PTT transitions were ever recorded, so when JTDX aborted a
+		// transmission mid-frame the log showed the abort and not the command
+		// that preceded it — the one thing needed to tell whether OpsLog answered
+		// something the client could not accept. Behind the same switch as the CAT
+		// wire trace: this is one line per poll and would drown an ordinary log.
+		if req != "" && cat.CIVTraceEnabled() {
+			s.log("rigctld: %s → %q ⇒ %q", c.RemoteAddr(), req, strings.TrimRight(resp, "\r\n"))
+		}
 		if resp != "" {
 			if _, err := w.WriteString(resp); err != nil {
 				return