fix: add network=host to dashboard buildx build step

Root cause confirmed: BuildKit sandbox creates isolated network namespace
that cannot resolve DNS even though the pod itself can. The buildx_flags
--driver-opt network=host only affects the buildkit daemon creation, not
the actual build steps. Adding network: host passes --network=host to
docker buildx build, making RUN steps use host networking.

.woodpecker/build-3.yml

@@ -198,6 +198,7 @@ steps:
       buildx_image: registry.celestium.life/dockerhub-cache/moby/buildkit:buildx-stable-1
       add_host: registry.celestium.life:10.1.1.12
       buildx_flags: --driver-opt network=host
+      network: host
       insecure: true
       buildkit_config: |
         [registry."registry.celestium.life"]