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/feishu.go

@@ -191,6 +191,12 @@ func (feishuConvertor) WorkflowJob(p *api.WorkflowJobPayload) (FeishuPayload, er
 	return newFeishuTextPayload(text), nil
 }
 
+func (feishuConvertor) WorkflowStep(p *api.WorkflowStepPayload) (FeishuPayload, error) {
+	text, _ := getWorkflowStepPayloadInfo(p, noneLinkFormatter, true)
+
+	return newFeishuTextPayload(text), nil
+}
+
 // feishuGenSign generates a signature for Feishu webhook
 // https://open.feishu.cn/document/client-docs/bot-v3/add-custom-bot
 func feishuGenSign(secret string, timestamp int64) string {