fix: use legacy Docker build to avoid permission errors in CI (#206)

- Replace BuildKit with legacy docker build (DOCKER_BUILDKIT=0)
- Use plain docker login instead of docker/login-action
- Remove BuildKit setup action entirely
- Works with VFS storage driver on unprivileged runners

Reviewed-on: graham/towerops-web#206

.forgejo/workflows/production.yaml

@@ -106,18 +106,9 @@ jobs:
             timeout 30 bash -c 'until docker info > /dev/null 2>&1; do sleep 1; done'
           fi
 
-      - name: Set up Docker Buildx
-        uses: https://github.com/docker/setup-buildx-action@v3
-        with:
-          driver: docker
-          install: true
-
       - name: Log in to Container Registry
-        uses: https://github.com/docker/login-action@v3
-        with:
-          registry: ${{ secrets.REGISTRY_URL }}
-          username: ${{ secrets.REGISTRY_USER }}
-          password: ${{ secrets.REGISTRY_PASSWORD }}
+        run: |
+          echo "${{ secrets.REGISTRY_PASSWORD }}" | docker login ${{ secrets.REGISTRY_URL }} -u "${{ secrets.REGISTRY_USER }}" --password-stdin
 
       - name: Generate image tag
         id: tag
@@ -130,16 +121,22 @@ jobs:
           echo "Full image tag: ${TAG}"
 
       - name: Build and push Docker image
-        uses: https://github.com/docker/build-push-action@v5
-        with:
-          context: .
-          file: k8s/Dockerfile
-          push: true
-          tags: |
-            ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:${{ steps.tag.outputs.tag }}
-            ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:production
-          build-args: |
-            MIX_ENV=prod
+        env:
+          DOCKER_BUILDKIT: 0
+        run: |
+          IMAGE_TAG="${{ steps.tag.outputs.tag }}"
+
+          # Build image
+          docker build \
+            --file k8s/Dockerfile \
+            --build-arg MIX_ENV=prod \
+            --tag ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:${IMAGE_TAG} \
+            --tag ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:production \
+            .
+
+          # Push both tags
+          docker push ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:${IMAGE_TAG}
+          docker push ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:production
 
       - name: Update deployment manifest
         run: |