Add language auto-detection

* adds langdetect as requirement for colab, standalone and textgen
* adds "auto" to the language dropdown in the Advanced Engine/Model Settings panel
* replace the hardcoded "en" by "auto" when called by the OpenAI compatible Speech API

system/requirements/requirements_standalone.txt

@@ -36,3 +36,4 @@ fastapi==0.112.2
 plotly==5.24.1
 scipy==1.14.1
 pyOpenSSL>=24.2.1
+langdetect>=1.0.9