refactor: encapsulate Docker build and tag logic within a script block in Jenkinsfile.

Jenkinsfile

@@ -54,11 +54,15 @@ pipeline {
         stage('Build & Tag') {
             steps {
                 withCredentials([string(credentialsId: GITEA_ID, variable: 'GITEA_TOKEN')]) {
-                    def fullImageName = "${DOCKER_HUB_USERNAME}/${IMAGE_NAME}"
+                    // Logic and variable definitions go inside 'script'
-                    sh "docker build --build-arg GITEA_TOKEN=${GITEA_TOKEN} -t ${fullImageName}:${IMAGE_TAG} ."
+                    script {
+                        def fullImageName = "${DOCKER_HUB_USERNAME}/${IMAGE_NAME}"
                         
-                    if (SECONDARY_TAG) {
+                        sh "docker build --build-arg GITEA_TOKEN=${GITEA_TOKEN} -t ${fullImageName}:${IMAGE_TAG} ."
-                        sh "docker tag ${fullImageName}:${IMAGE_TAG} ${fullImageName}:${SECONDARY_TAG}"
+                        
+                        if (SECONDARY_TAG) {
+                            sh "docker tag ${fullImageName}:${IMAGE_TAG} ${fullImageName}:${SECONDARY_TAG}"
+                        }
                     }
                 }
             }