Fix spurious disconnect after first message in GUI client

create_connection(timeout=5) left a 5-second read timeout on the
socket. Any collection interval longer than 5 s caused recv() to
raise socket.timeout, which was caught as OSError and reported as
a lost connection. Switch to blocking mode with settimeout(None)
immediately after the connect handshake.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

gui_client.py

@@ -54,6 +54,7 @@ class TcpReader(QObject):
         """Open connection; returns error string or None on success."""
         try:
             self._sock = socket.create_connection((host, port), timeout=5)
+            self._sock.settimeout(None)  # blocking reads after connect
         except OSError as exc:
             return str(exc)
         self._running = True