Show the print-failure snapshot in the device error dialog

When a print fails, DeviceErrorDialog now fetches the printer's captured camera
frame of the failure and shows it in place of the generic HMS illustration,
falling back to the local image and a drawn placeholder on older plugins or errors.

- Agent: add get_hms_snapshot through NetworkAgent / IPrinterAgent (BBL calls the
  bound plugin symbol; other agents no-op, so old plugins degrade gracefully).
- DeviceManager: parse and clear m_print_error_img_id from the print-error message.
- Dialog: tiered cloud/local/placeholder image reusing the single image widget,
  with a liveness-guarded async callback decoded on the UI thread.

src/slic3r/Utils/BBLPrinterAgent.cpp

@@ -171,6 +171,19 @@ int BBLPrinterAgent::request_bind_ticket(std::string* ticket)
     return -1;
 }
 
+int BBLPrinterAgent::get_hms_snapshot(std::string dev_id, std::string file_name, std::function<void(std::string, int)> callback)
+{
+    auto& plugin = BBLNetworkPlugin::instance();
+    auto agent = plugin.get_agent();
+    auto func = plugin.get_get_hms_snapshot();
+    // dev_id/file_name are passed as lvalues to bind the plugin's std::string& params.
+    // A null func (older plugin without this symbol) falls through to -1 so callers degrade gracefully.
+    if (func && agent) {
+        return func(agent, dev_id, file_name, callback);
+    }
+    return -1;
+}
+
 int BBLPrinterAgent::set_server_callback(OnServerErrFn fn)
 {
     auto& plugin = BBLNetworkPlugin::instance();