fix(i18n): 未登录 401 返回双语文案「登录状态已过期，请重新登录」

- auth_helpers.py / app_legacy.py 的 api_login_required 401 响应改用 tr('auth.session_expired')
- 新增 i18n key：zh 登录状态已过期，请重新登录 / en Your login session has expired. Please log in again.

modules/i18n_messages/api_auth.py

@@ -37,6 +37,10 @@ MESSAGES = {
         "zh-CN": "未登录",
         "en-US": "Not logged in",
     },
+    "auth.session_expired": {
+        "zh-CN": "登录状态已过期，请重新登录",
+        "en-US": "Your login session has expired. Please log in again.",
+    },
     "auth.host_mode_tutorial_not_applicable": {
         "zh-CN": "宿主机模式无需设置新手教程状态",
         "en-US": "Tutorial status does not apply in host mode",

server/app_legacy.py

@@ -821,7 +821,7 @@ def api_login_required(view_func):
     @wraps(view_func)
     def wrapped(*args, **kwargs):
         if not is_logged_in():
-            return jsonify({"error": "Unauthorized"}), 401
+            return jsonify({"error": tr("auth.session_expired")}), 401
         return view_func(*args, **kwargs)
 
     return wrapped

server/auth_helpers.py

@@ -34,7 +34,7 @@ def api_login_required(view_func):
     @wraps(view_func)
     def wrapped(*args, **kwargs):
         if not is_logged_in():
-            return jsonify({"error": "Unauthorized"}), 401
+            return jsonify({"error": tr("auth.session_expired")}), 401
         return view_func(*args, **kwargs)
     return wrapped