ci: fix node-runner docker, add image prune post-action

- Installs docker.io on node runner (base forgejo/runner:6 lacks it)
- Adds image prune step after push to clean unused images
- Squashes 5 previous failed CI attempts into single working fix

.gitea/workflows/build-push.yml

@@ -7,24 +7,19 @@ on:
 
 jobs:
   build-push:
-    runs-on: golang
-    container:
-      image: docker:27-cli
-      volumes:
-        - /docker-certs/client:/docker-certs/client:ro
+    runs-on: node
     env:
-      DOCKER_HOST: tcp://localhost:2376
-      DOCKER_TLS_VERIFY: "1"
-      DOCKER_CERT_PATH: /docker-certs/client
       REGISTRY: forgejo.riotpiao.com
       IMAGE: forgejo.riotpiao.com/rock/portfolio
     steps:
-      - name: Install git
-        run: apk add --no-cache git nodejs
-
       - name: Checkout code
         uses: actions/checkout@v4
 
+      - name: Install Docker client
+        run: |
+          apt-get update
+          apt-get install -y docker.io
+
       - name: Get short SHA
         id: sha
         run: |
@@ -64,4 +59,8 @@ jobs:
           docker push "${IMAGE}:latest"
           echo "✓ Image pushed: ${IMAGE}:${{ steps.sha.outputs.short_sha }}"
 
+      - name: Prune unused images
+        run: |
+          docker image prune -a --force 2>&1 | tail -3 || true
+