fix: set BuildKit worker networkMode=host for dashboard build

The BuildKit sandbox cannot resolve registry.npmjs.org DNS. Setting
networkMode=host in the worker config forces all RUN steps to use
the host network stack, which has confirmed internet access.

.woodpecker/build-3.yml

@@ -200,6 +200,8 @@ steps:
       buildx_flags: --driver-opt network=host --allow network.host
       insecure: true
       buildkit_config: |
+        [worker.oci]
+          networkMode = "host"
         [registry."registry.celestium.life"]
           insecure = true
         [registry."docker.io"]