feat(ops): 添加高级设置API支持

- 新增OpsAdvancedSettings数据模型
- 支持数据保留策略配置（错误日志、分钟级指标、小时级指标）
- 支持数据聚合开关配置
- 添加GET/PUT /admin/ops/advanced-settings接口
- 添加配置校验和默认值处理

相关文件：
- backend/internal/service/ops_settings_models.go
- backend/internal/service/ops_settings.go
- backend/internal/handler/admin/ops_settings_handler.go
- backend/internal/server/routes/admin.go
- backend/internal/service/domain_constants.go

backend/internal/service/domain_constants.go

@@ -143,6 +143,9 @@ const (
 
 	// SettingKeyOpsMetricsIntervalSeconds controls the ops metrics collector interval (>=60).
 	SettingKeyOpsMetricsIntervalSeconds = "ops_metrics_interval_seconds"
+
+	// SettingKeyOpsAdvancedSettings stores JSON config for ops advanced settings (data retention, aggregation).
+	SettingKeyOpsAdvancedSettings = "ops_advanced_settings"
 )
 
 // AdminAPIKeyPrefix is the prefix for admin API keys (distinct from user "sk-" keys).