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/types/index.ts

@@ -0,0 +1,148 @@
+// ============================================================
+// CamTalk 前端类型定义
+// 来源：docs/03-接口文档.md
+// ============================================================
+
+// ---- 会话模型 ----
+
+export interface SessionConfig {
+  ttsEnabled: boolean;
+  detailLevel: "low" | "high";
+  language: string;
+}
+
+export interface Session {
+  sessionId: string;
+  createdAt: string;
+  config: SessionConfig;
+}
+
+// ---- 聊天消息 ----
+
+export interface ChatMessage {
+  role: "user" | "assistant";
+  content: string;
+  imageUrl?: string;
+  timestamp: number;
+  tokensUsed?: number;
+}
+
+// ---- WebSocket 通用信封 ----
+
+export interface WsMessage {
+  type: string;
+  request_id?: string;
+  timestamp?: number;
+  [key: string]: unknown;
+}
+
+// ---- 客户端 → 服务端消息 ----
+
+export interface QueryMessage {
+  type: "query";
+  request_id: string;
+  image: string;       // Base64 JPEG（不含 data: 前缀）
+  audio: string;       // Base64 PCM 16kHz
+  mime_type?: string;  // 默认 "audio/pcm"
+}
+
+export interface ConfigMessage {
+  type: "config";
+  payload: {
+    tts_enabled?: boolean;
+    detail_level?: "low" | "high";
+    language?: string;
+  };
+}
+
+export interface InterruptMessage {
+  type: "interrupt";
+  request_id?: string;
+}
+
+export interface PingMessage {
+  type: "ping";
+}
+
+export type ClientMessage =
+  | QueryMessage
+  | ConfigMessage
+  | InterruptMessage
+  | PingMessage;
+
+// ---- 服务端 → 客户端消息 ----
+
+export interface ConnectedMessage {
+  type: "connected";
+  session_id: string;
+  server_version: string;
+}
+
+export interface STTResultMessage {
+  type: "stt_result";
+  request_id: string;
+  text: string;
+  is_final: boolean;
+}
+
+export interface LLMChunkMessage {
+  type: "llm_chunk";
+  request_id: string;
+  delta: string;
+  role: "assistant";
+}
+
+export interface LLMDoneMessage {
+  type: "llm_done";
+  request_id: string;
+  full_text: string;
+  tokens_used: {
+    prompt: number;
+    completion: number;
+    total: number;
+  };
+  model: string;
+  latency_ms: number;
+}
+
+export interface TTSAudioMessage {
+  type: "tts_audio";
+  request_id: string;
+  audio: string;       // Base64 音频片段
+  mime_type: string;   // "audio/mp3" 或 "audio/pcm"
+  is_last: boolean;
+}
+
+export interface ErrorMessage {
+  type: "error";
+  request_id?: string;
+  code: string;
+  message: string;
+}
+
+export interface PongMessage {
+  type: "pong";
+}
+
+export type ServerMessage =
+  | ConnectedMessage
+  | STTResultMessage
+  | LLMChunkMessage
+  | LLMDoneMessage
+  | TTSAudioMessage
+  | ErrorMessage
+  | PongMessage;
+
+// ---- 错误码 ----
+
+export type ErrorCode =
+  | "INVALID_MESSAGE"
+  | "SESSION_NOT_FOUND"
+  | "RATE_LIMITED"
+  | "IMAGE_TOO_LARGE"
+  | "AUDIO_TOO_SHORT"
+  | "LLM_TIMEOUT"
+  | "LLM_ERROR"
+  | "STT_ERROR"
+  | "TTS_ERROR"
+  | "INTERNAL_ERROR";