ci: speed up docker build with BuildKit cache mount and layer caching

.drone.yml

@@ -162,6 +162,8 @@ steps:
     volumes:
       - name: dockersock
         path: /var/run/docker.sock
+    environment:
+      DOCKER_BUILDKIT: "1"
     commands:
       - |
         echo "====== 开始构建 Docker 镜像 ======"
@@ -174,11 +176,20 @@ steps:
         fi
         echo "版本: $APP_VERSION"
 
+        # 拉取之前的镜像作为缓存来源（加速 layer 复用）
+        echo "正在拉取缓存镜像..."
+        docker pull "$IMAGE_NAME:latest" 2>/dev/null || true
+        docker pull "$LOCAL_HARBOR_REG/$LOCAL_HARBOR_PROJ/$IMAGE_NAME:latest" 2>/dev/null || true
+
+        # 使用 BuildKit 构建，启用缓存
         docker build \
-          -t "$IMAGE_NAME:$BUILD_VERSION" \
-          -t "$IMAGE_NAME:latest" \
+          --cache-from "$IMAGE_NAME:latest" \
+          --cache-from "$LOCAL_HARBOR_REG/$LOCAL_HARBOR_PROJ/$IMAGE_NAME:latest" \
+          --build-arg BUILDKIT_INLINE_CACHE=1 \
           --build-arg VERSION="$APP_VERSION" \
           --build-arg BUILD_TIME="$(TZ=Asia/Shanghai date '+%Y-%m-%d %H:%M')" \
+          -t "$IMAGE_NAME:$BUILD_VERSION" \
+          -t "$IMAGE_NAME:latest" \
           -f par-api/Dockerfile \
           .