Integrate product-ws voice demo on port 8000 alongside REST API.

Add src/voice Pipecat pipeline, browser demo at /voice-demo, and config/voice.json.

Co-authored-by: Cursor <cursoragent@cursor.com>

config/voice.json

@@ -0,0 +1,75 @@
+{
+  "server": {
+    "host": "0.0.0.0",
+    "port": 8000,
+    "cors_origins": ["http://localhost:3000", "http://localhost:8080"],
+    "serve_webpage": true,
+    "webpage_mount": "/voice-demo"
+  },
+  "audio": {
+    "sample_rate_hz": 16000,
+    "channels": 1,
+    "frame_ms": 20
+  },
+  "session": {
+    "inactivity_timeout_sec": 60
+  },
+  "turn": {
+    "vad": {
+      "confidence": 0.7,
+      "start_secs": 0.2,
+      "stop_secs": 0.4,
+      "min_volume": 0.6
+    },
+    "interruption_min_chars": 3,
+    "interruption_use_interim": true,
+    "interruption_short_replies": [
+      "是",
+      "是的",
+      "对",
+      "对的",
+      "嗯",
+      "好",
+      "好的",
+      "行",
+      "可以",
+      "没问题",
+      "不是",
+      "不",
+      "不行",
+      "不用",
+      "不要",
+      "没有",
+      "否"
+    ],
+    "user_speech_timeout_sec": 0.8
+  },
+  "agent": {
+    "system_prompt": "You are a helpful, friendly voice assistant. Keep responses concise and natural for spoken conversation.",
+    "greeting": "Please introduce yourself briefly.",
+    "greeting_mode": "generated"
+  },
+  "services": {
+    "stt": {
+      "provider": "openai",
+      "api_key": "",
+      "base_url": null,
+      "model": "gpt-4o-mini-transcribe",
+      "language": "en"
+    },
+    "llm": {
+      "provider": "openai",
+      "api_key": "",
+      "base_url": null,
+      "model": "gpt-4o-mini",
+      "temperature": 0.7
+    },
+    "tts": {
+      "provider": "openai",
+      "api_key": "",
+      "base_url": null,
+      "model": "gpt-4o-mini-tts",
+      "voice": "alloy"
+    }
+  }
+}