fix(ci): add default deploy environment variables for bash-safe pipeline

Reviewed-on: http://gitea.lan:3000/robbond/pleskSaas/pulls/40

Jenkinsfile

@@ -1,8 +1,3 @@
-def DEPLOY_SSH_CREDENTIAL_ID = env.DEPLOY_SSH_CREDENTIAL_ID ?: 'plesk-agency-deploy-key'
-def APP_HOST = env.APP_HOST ?: '192.168.68.89'
-def APP_USER = env.APP_USER ?: 'deploy'
-def DEPLOY_PATH = env.DEPLOY_PATH ?: '/opt/plesk-agency-portal'
-
 pipeline {
   // Build + deploy stages require Docker CLI/daemon access on the Jenkins node.
   // Ensure this label maps to an agent with Docker installed and usable.
@@ -12,6 +7,10 @@ pipeline {
     REGISTRY_IMAGE = "plesk-agency-portal"
     IMAGE_LATEST = "${REGISTRY_IMAGE}:latest"
     IMAGE_BUILD = "${REGISTRY_IMAGE}:build-${BUILD_NUMBER}"
+    DEPLOY_SSH_CREDENTIAL_ID = "${env.DEPLOY_SSH_CREDENTIAL_ID ?: 'plesk-agency-deploy-key'}"
+    APP_HOST = "${env.APP_HOST ?: '192.168.68.89'}"
+    APP_USER = "${env.APP_USER ?: 'deploy'}"
+    DEPLOY_PATH = "${env.DEPLOY_PATH ?: '/opt/plesk-agency-portal'}"
   }
 
   stages {
@@ -74,7 +73,7 @@ pipeline {
     stage('Deploy') {
       steps {
         withCredentials([sshUserPrivateKey(
-          credentialsId: DEPLOY_SSH_CREDENTIAL_ID,
+          credentialsId: "${env.DEPLOY_SSH_CREDENTIAL_ID}",
           keyFileVariable: 'SSH_KEY'
         )]) {
           sh '''