fix(stt): pass http_session to ElevenLabs STT plugin

Plugin requires explicit aiohttp session; livekit http_context not available
in this job setup.

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

voice.py

@@ -560,6 +560,7 @@ class VoiceSession:
                     api_key=ELEVENLABS_KEY,
                     model_id="scribe_v2_realtime",
                     language_code=os.environ.get("STT_LANGUAGE", "de"),
+                    http_session=self._http_session,
                 ),
                 llm=lk_openai.LLM(base_url=LITELLM_URL, api_key=LITELLM_KEY, model=self.model),
                 tts=elevenlabs.TTS(voice_id=voice_id, model="eleven_multilingual_v2",