fix: 배포 시 bootstrap/cache 디렉터리 생성 + slackSend 복구

- Stage/Production 배포에 mkdir -p bootstrap/cache 추가
- .gitignore로 누락되는 디렉터리 → composer install 시 package:discover 실패 해결
- rebase 중 사라진 slackSend 알림 복구 (Checkout, success, failure)

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

Jenkinsfile

@@ -30,6 +30,7 @@ pipeline {
 
                         ssh ${DEPLOY_USER}@211.117.60.189 '
                             cd /home/webservice/api-stage/releases/${RELEASE_ID} &&
+                            mkdir -p bootstrap/cache &&
                             ln -sfn /home/webservice/api-stage/shared/.env .env &&
                             ln -sfn /home/webservice/api-stage/shared/storage/app storage/app &&
                             composer install --no-dev --optimize-autoloader --no-interaction &&
@@ -76,6 +77,7 @@ pipeline {
 
                         ssh ${DEPLOY_USER}@211.117.60.189 '
                             cd /home/webservice/api/releases/${RELEASE_ID} &&
+                            mkdir -p bootstrap/cache &&
                             ln -sfn /home/webservice/api/shared/.env .env &&
                             ln -sfn /home/webservice/api/shared/storage/app storage/app &&
                             composer install --no-dev --optimize-autoloader --no-interaction &&