fix(ops): 修复告警状态验证和错误处理逻辑

- 增强告警事件状态验证，添加合法状态值检查
- 移除重试逻辑中的遗留字段赋值
- 修正仓库不可用时的错误类型
- 格式化测试文件代码

backend/internal/repository/scheduler_snapshot_outbox_integration_test.go

@@ -27,7 +27,7 @@ func TestSchedulerSnapshotOutboxReplay(t *testing.T) {
 		RunMode: config.RunModeStandard,
 		Gateway: config.GatewayConfig{
 			Scheduling: config.GatewaySchedulingConfig{
-				OutboxPollIntervalSeconds: 1,
+				OutboxPollIntervalSeconds:  1,
 				FullRebuildIntervalSeconds: 0,
 				DbFallbackEnabled:          true,
 			},