fix(mqtt): log a failed client start instead of reporting success

connect() logged "MQTT client started." unconditionally, so a failing
esp_mqtt_client_start() looked identical to a successful one. That is the one
state a later reconnect() cannot recover from, which made it the worst possible
line to be wrong.

lib/PsychicMqttClient/src/PsychicMqttClient.cpp

@@ -438,8 +438,13 @@ void PsychicMqttClient::connect()
     if (start_result == ESP_OK)
     {
         _started = true;
+        ESP_LOGI(TAG, "MQTT client started.");
+    }
+    else
+    {
+        // Reporting success here hides the one state reconnect() cannot recover from.
+        ESP_LOGE(TAG, "MQTT client failed to start: %s", esp_err_to_name(start_result));
     }
-    ESP_LOGI(TAG, "MQTT client started.");
 }
 
 void PsychicMqttClient::reconnect()