gui: fix reconnect after disconnect on same row

disconnect_receiver left the rid in _states, causing the duplicate-ID
check to fire on reconnect. Use remove_receiver instead (which cleans
up _states/_configs) and reset _rid to None.

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

gui/connection_tab.py

@@ -212,7 +212,8 @@ class ConnectionRow(QWidget):
     def _toggle(self):
         if self._connected:
             if self._rid:
-                self._model.disconnect_receiver(self._rid)
+                self._model.remove_receiver(self._rid)
+                self._rid = None
             return
 
         config = self.get_config()