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/webhook/msteams.go

@@ -346,6 +346,20 @@ func (msteamsConvertor) WorkflowJob(p *api.WorkflowJobPayload) (MSTeamsPayload,
 	), nil
 }
 
+func (msteamsConvertor) WorkflowStep(p *api.WorkflowStepPayload) (MSTeamsPayload, error) {
+	title, color := getWorkflowStepPayloadInfo(p, noneLinkFormatter, false)
+
+	return createMSTeamsPayload(
+		p.Repo,
+		p.Sender,
+		title,
+		"",
+		p.WorkflowJob.HTMLURL,
+		color,
+		&MSTeamsFact{"WorkflowStep:", p.Step.Name},
+	), nil
+}
+
 func createMSTeamsPayload(r *api.Repository, s *api.User, title, text, actionTarget string, color int, fact *MSTeamsFact) MSTeamsPayload {
 	facts := make([]MSTeamsFact, 0, 2)
 	if r != nil {