feat(gateway): 添加流超时处理机制

- 添加 StreamTimeoutSettings 配置结构体和系统设置
- 实现 TimeoutCounterCache Redis 计数器用于累计超时次数
- 在 RateLimitService 添加 HandleStreamTimeout 方法
- 在 gateway_service、openai_gateway_service、antigravity_gateway_service 中调用超时处理
- 添加后端 API 端点 GET/PUT /admin/settings/stream-timeout
- 添加前端配置界面到系统设置页面
- 支持配置：启用开关、超时阈值、处理方式、暂停时长、触发阈值、阈值窗口

默认配置：
- 启用：true
- 超时阈值：60秒
- 处理方式：临时不可调度
- 暂停时长：5分钟
- 触发阈值：3次
- 阈值窗口：10分钟

frontend/src/api/admin/settings.ts

@@ -201,6 +201,42 @@ export async function deleteAdminApiKey(): Promise<{ message: string }> {
   return data
 }
 
+/**
+ * Stream timeout settings interface
+ */
+export interface StreamTimeoutSettings {
+  enabled: boolean
+  timeout_seconds: number
+  action: 'temp_unsched' | 'error' | 'none'
+  temp_unsched_minutes: number
+  threshold_count: number
+  threshold_window_minutes: number
+}
+
+/**
+ * Get stream timeout settings
+ * @returns Stream timeout settings
+ */
+export async function getStreamTimeoutSettings(): Promise<StreamTimeoutSettings> {
+  const { data } = await apiClient.get<StreamTimeoutSettings>('/admin/settings/stream-timeout')
+  return data
+}
+
+/**
+ * Update stream timeout settings
+ * @param settings - Stream timeout settings to update
+ * @returns Updated settings
+ */
+export async function updateStreamTimeoutSettings(
+  settings: StreamTimeoutSettings
+): Promise<StreamTimeoutSettings> {
+  const { data } = await apiClient.put<StreamTimeoutSettings>(
+    '/admin/settings/stream-timeout',
+    settings
+  )
+  return data
+}
+
 export const settingsAPI = {
   getSettings,
   updateSettings,
@@ -208,7 +244,9 @@ export const settingsAPI = {
   sendTestEmail,
   getAdminApiKey,
   regenerateAdminApiKey,
-  deleteAdminApiKey
+  deleteAdminApiKey,
+  getStreamTimeoutSettings,
+  updateStreamTimeoutSettings
 }
 
 export default settingsAPI