Add env example

engine/.env.example

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+# Server Configuration
+HOST=0.0.0.0
+PORT=8000
+
+BACKEND_URL=http://127.0.0.1:8100
+
+# Audio Configuration
+SAMPLE_RATE=16000
+CHUNK_SIZE_MS=20
+
+# VAD Configuration
+VAD_THRESHOLD=0.5
+VAD_EOU_THRESHOLD_MS=600
+VAD_MIN_SPEECH_DURATION_MS=160
+
+# OpenAI / LLM Configuration (required for duplex voice)
+OPENAI_API_KEY=sk-fc4d59b360475f53401a864db8ce0985010acc4e696723d20a90d6569f38d80a
+OPENAI_API_URL=https://api.qnaigc.com/v1  # Optional: for Azure or compatible APIs
+LLM_MODEL=deepseek-v3
+LLM_TEMPERATURE=0.7
+
+# TTS Configuration
+TTS_PROVIDER=siliconflow
+TTS_VOICE=anna
+TTS_SPEED=1.0
+
+# SiliconFlow Configuration (for TTS and ASR)
+SILICONFLOW_API_KEY=sk-thmzysdpqqmhqxxshyqoxvjeiflexjdgaftyufrsgrhpjnyx
+SILICONFLOW_TTS_MODEL=FunAudioLLM/CosyVoice2-0.5B
+
+# ASR Configuration
+ASR_PROVIDER=siliconflow
+SILICONFLOW_ASR_MODEL=FunAudioLLM/SenseVoiceSmall
+ASR_INTERIM_INTERVAL_MS=500
+ASR_MIN_AUDIO_MS=300
+
+# Duplex Pipeline Configuration
+DUPLEX_ENABLED=true
+# DUPLEX_GREETING=Hello! How can I help you today?
+DUPLEX_SYSTEM_PROMPT=You are a helpful, friendly voice assistant. Keep your responses concise and conversational.
+
+# Barge-in Configuration
+# Minimum speech duration (ms) to trigger interruption - filters out brief noises
+# Lower = more sensitive (50-100ms recommended), Higher = filters more noise
+BARGE_IN_MIN_DURATION_MS=100
+
+ASR_START_MIN_SPEECH_MS=100
+ASR_PRE_SPEECH_MS=320
+
+# Logging
+LOG_LEVEL=INFO
+LOG_FORMAT=text
+