feat: add --debug tracing to hendi_ctrl_app.py, document v1.16 fix

HendiCtrl.cmd() previously raised a bare "Communication error" for any
non-OK response, discarding the firmware's actual reply. It now
includes the raw echo/answer bytes, and --debug prints every
request/response. Using this, the rejected R1 during lockout turned
out to be an explicit "ERR:Invalid state" reply, not a timeout.

Also flashed and retested v1.16: plain reconnect (no --reset) now
recovers from the lockout reliably (4/4 trials), fixing the
intermittent behavior seen on v1.15.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GpePKZiEZWbGo9HrfuML6U

scripts/hendi_ctrl_app.py

@@ -67,6 +67,7 @@ def main():
 	parser = ap.ArgumentParser(description=__doc__)
 	parser.add_argument("--serial-port", default=DEFAULT_PORT)
 	parser.add_argument("--baudrate", type=int, default=DEFAULT_BAUDRATE)
+	parser.add_argument("--debug", action="store_true", help="print raw request/response bytes for every command")
 	parser.add_argument("--reset", action="store_true", help="toggle the reset line (does not clear the ungraceful-disconnect lockout - use the device's knob for that)")
 	parser.add_argument("--version", action="store_true", help="print software identifier/version")
 	parser.add_argument("--capabilities", action="store_true", help="print power/digit capability info")
@@ -77,7 +78,7 @@ def main():
 	parser.add_argument("--update-firmware", metavar="FILE", help="flash the given firmware file")
 	args = parser.parse_args()
 
-	hendi = HendiCtrl(args.serial_port, args.baudrate)
+	hendi = HendiCtrl(args.serial_port, args.baudrate, debug=args.debug)
 
 	if args.reset:
 		reset(hendi)