chore: add pipeline

Jenkinsfile

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+pipeline {
+  agent any
+  environment {
+    REGISTRY = 'registry.bstein.dev'
+    IMAGE    = 'infra/harbor-arm-build'
+  }
+  stages {
+    stage('Checkout') {
+      steps {
+        git credentialsId: 'gitea-pat', url: 'https://scm.bstein.dev/bstein/harbor-arm-build.git'
+      }
+    }
+    stage('Build image') {
+      steps {
+        sh '''
+        cat > app.sh <<'APP'
+        #!/usr/bin/env bash
+        echo "hello harbor arm build $(date)"
+        APP
+        chmod +x app.sh
+        cat > Dockerfile <<'DOCKER'
+        FROM alpine:3.20
+        COPY app.sh /usr/local/bin/app.sh
+        RUN chmod +x /usr/local/bin/app.sh
+        ENTRYPOINT ["/usr/local/bin/app.sh"]
+        DOCKER
+        docker build -t $REGISTRY/$IMAGE:latest .
+        '''
+      }
+    }
+    stage('Push image') {
+      steps {
+        withCredentials([usernamePassword(credentialsId: 'harbor-robot', usernameVariable: 'HUSER', passwordVariable: 'HPASS')]) {
+          sh '''
+          echo "$HPASS" | docker login -u "$HUSER" --password-stdin $REGISTRY
+          docker push $REGISTRY/$IMAGE:latest
+          '''
+        }
+      }
+    }
+  }
+}

README.md

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+# harbor-arm-build
+Proof-of-concept Jenkins pipeline: build a tiny image and push to Harbor.