Fix device popup, mapping, and status-parse defects

- Allow mapping to EMPTY trays only from the multi-machine send page and keep
  both panels pickable in the LEFT_AND_RIGHT view
- Guard the error-dialog cloud snapshot against stale callbacks and fall back
  to the local illustration on timeout
- Parse the ipcam storage-check ack and axis/chamber pushes defensively
- Strip fan-control telemetry, initialize the upgrade error code, restore the
  .json filter in the model-id scan
- Fix best-position popup tray lookup, gradient placement, and colour-list
  ownership
- Cover switch binding sets and invalid-track transients in DevMapping tests

src/slic3r/GUI/DeviceCore/DevConfigUtil.cpp

@@ -61,6 +61,8 @@ std::map<std::string, std::string> DevPrinterConfigUtil::get_all_model_id_with_n
 
         for (wxString file : m_files)
         {
+            if (!file.Lower().ends_with(".json")) continue;
+
             std::string config_file = m_resource_file_path + "/printers/" + file.ToStdString();
             boost::nowide::ifstream json_file(config_file.c_str());