fix(idgen): retry snowflake generation and error on negative ID

NextUint64ID now retries up to 3 times when Int64() is negative, then
returns an error instead of 0 or Fatalf. All call sites propagate the
error to avoid GORM omitting zero-value primary keys.

internal/model/task_execution.go

@@ -60,7 +60,11 @@ func (TaskExecution) TableName() string {
 
 // CreateTaskExecution 创建任务执行记录
 func CreateTaskExecution(ctx context.Context, execution *TaskExecution) error {
-	execution.ID = idgen.NextUint64ID()
+	id, err := idgen.NextUint64ID()
+	if err != nil {
+		return err
+	}
+	execution.ID = id
 	return db.DB(ctx).Create(execution).Error
 }