Use Ubuntu container with Node.js and buildah for CI

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.forgejo/workflows/docker.yaml

@@ -7,8 +7,13 @@ jobs:
   build:
     runs-on: docker
     container:
-      image: quay.io/buildah/stable
+      image: ubuntu:24.04
     steps:
+      - name: Install dependencies
+        run: |
+          apt-get update -q
+          apt-get install -qy nodejs buildah
+
       - uses: actions/checkout@v4
 
       - name: Build and push Docker image