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/App.tsx

@@ -0,0 +1,72 @@
+// ============================================================
+// CamTalk — 主应用组件
+// ============================================================
+
+import { useVisionSession } from "./hooks/useVisionSession";
+import { VideoPreview } from "./components/VideoPreview";
+import { ChatPanel } from "./components/ChatPanel";
+import "./App.css";
+
+function App() {
+  const {
+    messages,
+    currentReply,
+    isProcessing,
+    isSpeaking,
+    connectionStatus,
+    videoRef,
+    stream,
+    startSession,
+    stopSession,
+    interrupt,
+  } = useVisionSession();
+
+  return (
+    <div className="app">
+      <header className="app-header">
+        <h1>CamTalk</h1>
+        <span className={`status status--${connectionStatus}`}>
+          {connectionStatus === "connected" ? "已连接" : connectionStatus === "connecting" ? "连接中..." : "未连接"}
+        </span>
+      </header>
+
+      <main className="app-main">
+        <div className="video-section">
+          <VideoPreview ref={videoRef} isStreaming={!!stream} />
+          {isSpeaking && <div className="vad-indicator">🎤 正在聆听...</div>}
+        </div>
+
+        <div className="chat-section">
+          <ChatPanel messages={messages} />
+          {currentReply && (
+            <div className="chat-message chat-message--assistant chat-message--streaming">
+              <div className="chat-message__role">AI</div>
+              <div className="chat-message__content">{currentReply}</div>
+            </div>
+          )}
+        </div>
+      </main>
+
+      <footer className="app-footer">
+        {connectionStatus !== "connected" ? (
+          <button className="btn btn--primary" onClick={startSession}>
+            开始对话
+          </button>
+        ) : (
+          <>
+            <button className="btn btn--secondary" onClick={stopSession}>
+              结束对话
+            </button>
+            {isProcessing && (
+              <button className="btn btn--warning" onClick={interrupt}>
+                打断
+              </button>
+            )}
+          </>
+        )}
+      </footer>
+    </div>
+  );
+}
+
+export default App;