ci: Jenkinsfile slackSend 알림 복구

- Checkout: slackSend 빌드 시작 알림 추가 (tokenCredentialId)
- Post success/failure: echo → slackSend 교체 (tokenCredentialId)
- 이전 rebase 과정에서 소실된 slackSend 복구

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

Jenkinsfile

@@ -8,7 +8,11 @@ pipeline {
 
     stages {
         stage('Checkout') {
-            steps { checkout scm }
+            steps {
+                slackSend channel: '#product_infra', color: '#439FE0', tokenCredentialId: 'slack-token',
+                    message: "🚀 *api* 빌드 시작 (`${env.BRANCH_NAME}`)\n<${env.BUILD_URL}|빌드 #${env.BUILD_NUMBER}>"
+                checkout scm
+            }
         }
 
         // ── main → 운영서버 Stage 배포 ──
@@ -99,9 +103,13 @@ pipeline {
     }
 
     post {
-        success { echo "✅ api 배포 완료 (${env.BRANCH_NAME})" }
+        success {
+            slackSend channel: '#product_infra', color: 'good', tokenCredentialId: 'slack-token',
+                message: "✅ *api* 배포 성공 (`${env.BRANCH_NAME}`)\n<${env.BUILD_URL}|빌드 #${env.BUILD_NUMBER}>"
+        }
         failure {
-            echo "❌ api 배포 실패 (${env.BRANCH_NAME})"
+            slackSend channel: '#product_infra', color: 'danger', tokenCredentialId: 'slack-token',
+                message: "❌ *api* 배포 실패 (`${env.BRANCH_NAME}`)\n<${env.BUILD_URL}|빌드 #${env.BUILD_NUMBER}>"
             script {
                 if (env.BRANCH_NAME == 'main') {
                     sshagent(credentials: ['deploy-ssh-key']) {