Drop buildx, use plain docker build/push

docker/setup-buildx-action resolves its builder endpoint from the
docker context file rather than the live DOCKER_HOST env var, so it
still tried the (absent) unix socket. Plain docker CLI commands
honor DOCKER_HOST directly, matching what the runner now provides.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.forgejo/workflows/build.yml

@@ -8,10 +8,11 @@ on:
 jobs:
   build-and-push:
     runs-on: docker
-    # actions/checkout & co. are JS actions and need Node, so the job
-    # container has to be a Node image (not a bare docker CLI image). The
-    # runner already provides a privileged container wired up to its own
-    # dind sidecar via DOCKER_HOST, so we just need the docker CLI itself.
+    # actions/checkout is a JS action and needs Node, so the job container
+    # has to be a Node image. The runner already provides a privileged
+    # container wired up to its own dind sidecar via DOCKER_HOST, so we
+    # just need the docker CLI itself. Plain `docker` commands (rather
+    # than buildx-based actions) pick up DOCKER_HOST directly.
     container: node:20-bookworm
     steps:
       - name: Checkout
@@ -27,24 +28,17 @@ jobs:
           echo "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/debian $(. /etc/os-release && echo $VERSION_CODENAME) stable" \
             > /etc/apt/sources.list.d/docker.list
           apt-get update
-          apt-get install -y --no-install-recommends docker-ce-cli docker-buildx-plugin
+          apt-get install -y --no-install-recommends docker-ce-cli
 
       - name: Log in to Forgejo registry
-        uses: docker/login-action@v3
-        with:
-          registry: git.rosenvold.tech
-          username: ${{ github.actor }}
-          password: ${{ secrets.GITHUB_TOKEN }}
+        run: echo "${{ secrets.GITHUB_TOKEN }}" | docker login git.rosenvold.tech -u "${{ github.actor }}" --password-stdin
 
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
+      - name: Build image
+        run: |
+          docker build \
+            -t git.rosenvold.tech/lucas/rosenvold-core:latest \
+            -t git.rosenvold.tech/lucas/rosenvold-core:${{ github.sha }} \
+            -f Containerfile .
 
-      - name: Build and push
-        uses: docker/build-push-action@v5
-        with:
-          context: .
-          file: ./Containerfile
-          push: true
-          tags: |
-            git.rosenvold.tech/lucas/rosenvold-core:latest
-            git.rosenvold.tech/lucas/rosenvold-core:${{ github.sha }}
+      - name: Push image
+        run: docker push git.rosenvold.tech/lucas/rosenvold-core --all-tags