ci: fix docker dind access, remove container override

Problem: Push job used docker:27-cli override with explicit dind cert
mounting, but runner base changed to code.forgejo.org/forgejo/runner:6.
Alpine container couldn't access Debian runner's dind socket paths.

Fix:
- Remove container override, run on golang runner natively
- Install docker.io directly in push step (apt-get)
- Add docker image prune post-action to cleanup

This pattern matches riotpiao.com CI and works with current runner setup.

.gitea/workflows/ci.yaml

@@ -42,17 +42,15 @@ jobs:
     needs: verify
     if: github.ref == 'refs/heads/main' && github.event_name == 'push'
     runs-on: golang
-    container:
-      image: docker:27-cli
-      volumes:
-        - /docker-certs/client:/docker-certs/client:ro
-    env:
-      DOCKER_HOST: tcp://localhost:2376
-      DOCKER_TLS_VERIFY: "1"
-      DOCKER_CERT_PATH: /docker-certs/client
     steps:
-      - name: install node (required by JS-based actions)
+      - name: Install dependencies
-        run: apk add --no-cache nodejs git
+        run: |
+          apt-get update
+          apt-get install -y --no-install-recommends \
+            docker.io \
+            nodejs \
+            git
+          rm -rf /var/lib/apt/lists/*
 
       - uses: actions/checkout@v4
 
@@ -81,3 +79,8 @@ jobs:
         run: |
           docker push "${IMAGE}:${{ steps.sha.outputs.short_sha }}"
           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