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

backend/internal/handler/admin/setting_handler.go

@@ -654,3 +654,72 @@ func (h *SettingHandler) DeleteAdminAPIKey(c *gin.Context) {
 
 	response.Success(c, gin.H{"message": "Admin API key deleted"})
 }
+
+// GetStreamTimeoutSettings 获取流超时处理配置
+// GET /api/v1/admin/settings/stream-timeout
+func (h *SettingHandler) GetStreamTimeoutSettings(c *gin.Context) {
+	settings, err := h.settingService.GetStreamTimeoutSettings(c.Request.Context())
+	if err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+
+	response.Success(c, dto.StreamTimeoutSettings{
+		Enabled:                settings.Enabled,
+		TimeoutSeconds:         settings.TimeoutSeconds,
+		Action:                 settings.Action,
+		TempUnschedMinutes:     settings.TempUnschedMinutes,
+		ThresholdCount:         settings.ThresholdCount,
+		ThresholdWindowMinutes: settings.ThresholdWindowMinutes,
+	})
+}
+
+// UpdateStreamTimeoutSettingsRequest 更新流超时配置请求
+type UpdateStreamTimeoutSettingsRequest struct {
+	Enabled                bool   `json:"enabled"`
+	TimeoutSeconds         int    `json:"timeout_seconds"`
+	Action                 string `json:"action"`
+	TempUnschedMinutes     int    `json:"temp_unsched_minutes"`
+	ThresholdCount         int    `json:"threshold_count"`
+	ThresholdWindowMinutes int    `json:"threshold_window_minutes"`
+}
+
+// UpdateStreamTimeoutSettings 更新流超时处理配置
+// PUT /api/v1/admin/settings/stream-timeout
+func (h *SettingHandler) UpdateStreamTimeoutSettings(c *gin.Context) {
+	var req UpdateStreamTimeoutSettingsRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		response.BadRequest(c, "Invalid request: "+err.Error())
+		return
+	}
+
+	settings := &service.StreamTimeoutSettings{
+		Enabled:                req.Enabled,
+		TimeoutSeconds:         req.TimeoutSeconds,
+		Action:                 req.Action,
+		TempUnschedMinutes:     req.TempUnschedMinutes,
+		ThresholdCount:         req.ThresholdCount,
+		ThresholdWindowMinutes: req.ThresholdWindowMinutes,
+	}
+
+	if err := h.settingService.SetStreamTimeoutSettings(c.Request.Context(), settings); err != nil {
+		response.BadRequest(c, err.Error())
+		return
+	}
+
+	// 重新获取设置返回
+	updatedSettings, err := h.settingService.GetStreamTimeoutSettings(c.Request.Context())
+	if err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+
+	response.Success(c, dto.StreamTimeoutSettings{
+		Enabled:                updatedSettings.Enabled,
+		TimeoutSeconds:         updatedSettings.TimeoutSeconds,
+		Action:                 updatedSettings.Action,
+		TempUnschedMinutes:     updatedSettings.TempUnschedMinutes,
+		ThresholdCount:         updatedSettings.ThresholdCount,
+		ThresholdWindowMinutes: updatedSettings.ThresholdWindowMinutes,
+	})
+}