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

Jenkinsfile

@@ -54,7 +54,10 @@ pipeline {
         stage('Build & Tag') {
             steps {
                 withCredentials([string(credentialsId: GITEA_ID, variable: 'GITEA_TOKEN')]) {
+                    // Logic and variable definitions go inside 'script'
+                    script {
                         def fullImageName = "${DOCKER_HUB_USERNAME}/${IMAGE_NAME}"
+                        
                         sh "docker build --build-arg GITEA_TOKEN=${GITEA_TOKEN} -t ${fullImageName}:${IMAGE_TAG} ."
                         
                         if (SECONDARY_TAG) {
@@ -63,6 +66,7 @@ pipeline {
                     }
                 }
             }
+        }
 
         stage('Push to Docker Hub') {
             steps {