feat(webhook): add workflow_step webhook events for step-level CI notifications

Adds HookEventWorkflowStep event type that fires on every step state
transition (queued -> in_progress -> completed). Follows the same
pattern as the existing workflow_job events.

- New WorkflowStepPayload struct with run/job/step context
- WorkflowStepStatusUpdate notifier interface + dispatch
- Step state change detection in UpdateTask runner endpoint
- Fix: register workflow_step in updateHookEvents API mapping
- Full test coverage mirroring workflow_job tests

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/actions/notify.go

@@ -119,6 +119,30 @@ func NotifyWorkflowJobsStatusUpdate(ctx context.Context, jobs ...*actions_model.
 	}
 }
 
+// NotifyWorkflowStepStatusUpdate notifies a single step status update when a concrete task is available.
+// Use it when a step transitions between queued, in_progress, and completed states.
+func NotifyWorkflowStepStatusUpdate(ctx context.Context, job *actions_model.ActionRunJob, task *actions_model.ActionTask, step *actions_model.ActionTaskStep) {
+	if job.RunAttemptID == 0 {
+		if err := job.LoadAttributes(ctx); err != nil {
+			log.Error("job.LoadAttributes: %v", err)
+			return
+		}
+		notify_service.WorkflowStepStatusUpdate(ctx, job.Run.Repo, job.Run.TriggerUser, job, task, step)
+		return
+	}
+
+	attempt, err := actions_model.GetRunAttemptByRepoAndID(ctx, job.RepoID, job.RunAttemptID)
+	if err != nil {
+		log.Error("GetRunAttemptByRepoAndID: %v", err)
+		return
+	}
+	if err := attempt.LoadAttributes(ctx); err != nil {
+		log.Error("attempt.LoadAttributes: %v", err)
+		return
+	}
+	notify_service.WorkflowStepStatusUpdate(ctx, attempt.Run.Repo, attempt.TriggerUser, job, task, step)
+}
+
 // NotifyWorkflowJobStatusUpdateWithTask notifies a single job status update when a concrete task is available.
 // Use it for runner/task lifecycle callbacks so the notification includes the originating task context.
 func NotifyWorkflowJobStatusUpdateWithTask(ctx context.Context, job *actions_model.ActionRunJob, task *actions_model.ActionTask) {