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/components/AuthPage/index.tsx

@@ -0,0 +1,130 @@
+// ============================================================
+// AuthPage — 登录 / 注册页面
+// 职责：用户认证表单，支持登录和注册模式切换
+// ============================================================
+
+import { useCallback, useState } from "react";
+import { useAuth } from "../../lib/auth";
+import { useI18n } from "../../lib/i18n";
+
+type AuthMode = "login" | "register";
+
+export function AuthPage() {
+  const { login, register } = useAuth();
+  const { t } = useI18n();
+  const [mode, setMode] = useState<AuthMode>("login");
+  const [username, setUsername] = useState("");
+  const [password, setPassword] = useState("");
+  const [error, setError] = useState("");
+  const [isSubmitting, setIsSubmitting] = useState(false);
+
+  const handleSubmit = useCallback(
+    async (e: React.FormEvent) => {
+      e.preventDefault();
+      setError("");
+
+      // 前端校验
+      if (username.length < 3 || username.length > 64) {
+        setError(t("auth.error.usernameLength"));
+        return;
+      }
+      if (password.length < 8 || password.length > 72) {
+        setError(t("auth.error.passwordLength"));
+        return;
+      }
+
+      setIsSubmitting(true);
+      const fn = mode === "login" ? login : register;
+      const result = await fn(username, password);
+      setIsSubmitting(false);
+
+      if (result.error) {
+        setError(result.error);
+      }
+    },
+    [username, password, mode, login, register, t]
+  );
+
+  const toggleMode = useCallback(() => {
+    setMode((m) => (m === "login" ? "register" : "login"));
+    setError("");
+  }, []);
+
+  return (
+    <div className="auth-page">
+      <div className="auth-card">
+        <div className="auth-card__header">
+          <h1 className="auth-card__logo">CamTalk</h1>
+          <p className="auth-card__subtitle">{t("auth.subtitle")}</p>
+        </div>
+
+        <form className="auth-form" onSubmit={handleSubmit}>
+          <div className="auth-form__tabs">
+            <button
+              type="button"
+              className={`auth-tab ${mode === "login" ? "auth-tab--active" : ""}`}
+              onClick={() => { setMode("login"); setError(""); }}
+            >
+              {t("auth.login")}
+            </button>
+            <button
+              type="button"
+              className={`auth-tab ${mode === "register" ? "auth-tab--active" : ""}`}
+              onClick={() => { setMode("register"); setError(""); }}
+            >
+              {t("auth.register")}
+            </button>
+          </div>
+
+          <div className="auth-form__fields">
+            <label className="auth-field">
+              <span className="auth-field__label">{t("auth.username")}</span>
+              <input
+                type="text"
+                className="auth-field__input"
+                value={username}
+                onChange={(e) => setUsername(e.target.value)}
+                placeholder={t("auth.username.placeholder")}
+                autoComplete="username"
+                autoFocus
+              />
+            </label>
+
+            <label className="auth-field">
+              <span className="auth-field__label">{t("auth.password")}</span>
+              <input
+                type="password"
+                className="auth-field__input"
+                value={password}
+                onChange={(e) => setPassword(e.target.value)}
+                placeholder={t("auth.password.placeholder")}
+                autoComplete={mode === "login" ? "current-password" : "new-password"}
+              />
+            </label>
+          </div>
+
+          {error && <div className="auth-form__error">{error}</div>}
+
+          <button
+            type="submit"
+            className="auth-form__submit"
+            disabled={isSubmitting}
+          >
+            {isSubmitting
+              ? t("auth.submitting")
+              : mode === "login"
+                ? t("auth.login")
+                : t("auth.register")}
+          </button>
+        </form>
+
+        <p className="auth-card__footer">
+          {mode === "login" ? t("auth.noAccount") : t("auth.hasAccount")}
+          <button className="auth-card__link" onClick={toggleMode}>
+            {mode === "login" ? t("auth.register") : t("auth.login")}
+          </button>
+        </p>
+      </div>
+    </div>
+  );
+}

frontend/src/components/WebSocketManager/index.tsx

@@ -25,7 +25,7 @@ export function useWebSocketManager() {
   return {
     status,
     lastMessage,
-    connect: () => wsClient.connect(),
+    connect: (token?: string) => wsClient.connect(token),
     disconnect: () => wsClient.disconnect(),
     send: wsClient.send.bind(wsClient),
   };