feat: 初始化前端项目，搭建 React + TypeScript + Vite 工程结构

- 创建 Vite + React 18 + TypeScript 项目（严格模式）
- 安装 @ricky0123/vad-web、onnxruntime-web、uuid 依赖
- 定义全部 WebSocket 消息类型和数据模型（对齐接口文档）
- 实现 WebSocket 连接管理（心跳保活、指数退避重连）
- 实现音频编码工具（PCM↔Base64、DataURL 转换）
- 创建组件骨架：CameraManager、MicManager、EdgeProcessor、WebSocketManager、ChatPanel、VideoPreview
- 实现核心 useVisionSession Hook 骨架
- 配置 ESLint（_前缀变量忽略规则）

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

frontend/src/components/MicManager/index.tsx

@@ -0,0 +1,51 @@
+// ============================================================
+// MicManager — 麦克风音频采集
+// 职责：获取麦克风 MediaStream，供 VAD 和音频录制使用
+// ============================================================
+
+import { useCallback, useRef, useState } from "react";
+
+export function useMicrophone() {
+  const [stream, setStream] = useState<MediaStream | null>(null);
+  const [error, setError] = useState<string | null>(null);
+  const audioContextRef = useRef<AudioContext | null>(null);
+
+  const startMic = useCallback(async () => {
+    try {
+      const mediaStream = await navigator.mediaDevices.getUserMedia({
+        audio: {
+          sampleRate: 16000,
+          channelCount: 1,
+          echoCancellation: true,
+          noiseSuppression: true,
+        },
+        video: false,
+      });
+      setStream(mediaStream);
+      setError(null);
+      return mediaStream;
+    } catch (err) {
+      const message = err instanceof Error ? err.message : "无法访问麦克风";
+      setError(message);
+      console.error("[Mic] 获取麦克风失败:", err);
+      return null;
+    }
+  }, []);
+
+  const stopMic = useCallback(() => {
+    stream?.getTracks().forEach((track) => track.stop());
+    setStream(null);
+    audioContextRef.current?.close();
+    audioContextRef.current = null;
+  }, [stream]);
+
+  /** 获取或创建 AudioContext */
+  const getAudioContext = useCallback((): AudioContext => {
+    if (!audioContextRef.current) {
+      audioContextRef.current = new AudioContext({ sampleRate: 16000 });
+    }
+    return audioContextRef.current;
+  }, []);
+
+  return { stream, error, startMic, stopMic, getAudioContext };
+}