Wire cloud STT/TTS providers into pipeline

- Add provider field to STTConfig and TTSConfig (deepgram/venice)
- Add VeniceTTSConfig model for venice voice/base_url settings
- Add CloudTTSSynthesizer adapter wrapping VeniceKokoroTTS
- Loosen STTTranscriber type hint to accept any engine with transcribe_async
- Update run.py to use create_stt_engine/create_tts_engine factories
- Provider-based init: reads config.pipeline.stt.provider and .tts.provider
- Fix duplicate language key in config.yaml
- Remove duplicate language field from STT config

Cloud-only path: VAD (local) -> Deepgram STT -> OpenClaw -> Venice TTS -> Discord

config.yaml

@@ -123,9 +123,6 @@ pipeline:
     compute_type: "float16"
     beam_size: 1
 
-    # Language hint (null = auto-detect)
-    language: "en"
-
     # VAD filter (use built-in VAD in whisper)
     vad_filter: false