Add Jenkins pipeline for CI/CD process

This Jenkinsfile defines a CI/CD pipeline with stages for checkout, build, test, and publish, along with success and failure messages.

Jenkinsfile

@@ -0,0 +1,43 @@
+pipeline {
+    agent any
+
+    environment {
+        GITHUB_ACTOR = 'jakubbbdev'
+        GITHUB_TOKEN = credentials('github-credentials')
+    }
+
+    stages {
+        stage('Checkout') {
+            steps {
+                checkout scm
+            }
+        }
+
+        stage('Build') {
+            steps {
+                sh './gradlew build'
+            }
+        }
+
+        stage('Test') {
+            steps {
+                sh './gradlew test'
+            }
+        }
+
+        stage('Publish') {
+            steps {
+                sh './gradlew publish'
+            }
+        }
+    }
+
+    post {
+        success {
+            echo '✅ Build erfolgreich!'
+        }
+        failure {
+            echo '❌ Build fehlgeschlagen!'
+        }
+    }
+}