feat: 实现前端认证系统，WebSocket 连接携带 JWT token

- 新增 AuthContext/AuthProvider：登录/注册状态管理，JWT 自动刷新
- 新增 AuthPage 组件：登录/注册表单，支持模式切换和前端校验
- 新增 api.ts：封装 auth REST API 客户端（register/login/refresh/logout）
- WebSocket 连接时拼接 ?token=<jwt>，重连自动携带
- useVisionSession 接受 accessToken 参数并透传
- App.tsx 包裹 AuthProvider，未登录时显示登录页
- storage.ts 新增 token/user 的 localStorage 存储
- i18n 新增中/英/日三语 auth 翻译
- App.css 新增 auth 页面和用户 badge 样式

frontend/src/lib/storage.ts

@@ -7,6 +7,9 @@ import type { ChatMessage, SessionConfig, SessionSummary, Theme } from "../types
 
 const CONFIG_KEY = "camtalk:config";
 const THEME_KEY = "camtalk:theme";
+const ACCESS_TOKEN_KEY = "camtalk:access_token";
+const REFRESH_TOKEN_KEY = "camtalk:refresh_token";
+const USER_KEY = "camtalk:user";
 
 const DEFAULT_CONFIG: SessionConfig = {
   ttsEnabled: true,
@@ -100,3 +103,70 @@ export function deleteSessionMessages(sessionId: string): void {
     localStorage.removeItem(SESSION_MSG_PREFIX + sessionId);
   } catch { /* ignore */ }
 }
+
+// ---- Auth Token 存储 ----
+
+export interface StoredUser {
+  id: string;
+  username: string;
+  created_at: string;
+}
+
+/** 保存 access token */
+export function saveAccessToken(token: string): void {
+  try {
+    localStorage.setItem(ACCESS_TOKEN_KEY, token);
+  } catch { /* ignore */ }
+}
+
+/** 获取 access token */
+export function loadAccessToken(): string | null {
+  try {
+    return localStorage.getItem(ACCESS_TOKEN_KEY);
+  } catch {
+    return null;
+  }
+}
+
+/** 保存 refresh token */
+export function saveRefreshToken(token: string): void {
+  try {
+    localStorage.setItem(REFRESH_TOKEN_KEY, token);
+  } catch { /* ignore */ }
+}
+
+/** 获取 refresh token */
+export function loadRefreshToken(): string | null {
+  try {
+    return localStorage.getItem(REFRESH_TOKEN_KEY);
+  } catch {
+    return null;
+  }
+}
+
+/** 保存用户信息 */
+export function saveUser(user: StoredUser): void {
+  try {
+    localStorage.setItem(USER_KEY, JSON.stringify(user));
+  } catch { /* ignore */ }
+}
+
+/** 获取用户信息 */
+export function loadUser(): StoredUser | null {
+  try {
+    const raw = localStorage.getItem(USER_KEY);
+    if (!raw) return null;
+    return JSON.parse(raw) as StoredUser;
+  } catch {
+    return null;
+  }
+}
+
+/** 清除所有 auth 数据 */
+export function clearAuth(): void {
+  try {
+    localStorage.removeItem(ACCESS_TOKEN_KEY);
+    localStorage.removeItem(REFRESH_TOKEN_KEY);
+    localStorage.removeItem(USER_KEY);
+  } catch { /* ignore */ }
+}