T-3: switch from Buildah to Docker for image build

The act_runner does not have Buildah installed. Docker is available
via socket forwarding, so use docker build/tag/push instead.

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

.gitea/workflows/ci.yaml

@@ -74,19 +74,16 @@ jobs:
           REGISTRY="${REGISTRY#http://}"
           REPO="${{ github.repository }}"
           IMAGE="${REGISTRY}/${REPO}"
-          buildah bud -t "${IMAGE}:${{ steps.semver.outputs.full }}" .
-          buildah tag "${IMAGE}:${{ steps.semver.outputs.full }}" \
-            "${IMAGE}:${{ steps.semver.outputs.minor }}" \
-            "${IMAGE}:${{ steps.semver.outputs.major }}" \
-            "${IMAGE}:latest"
+          docker build -t "${IMAGE}:${{ steps.semver.outputs.full }}" .
+          docker tag "${IMAGE}:${{ steps.semver.outputs.full }}" "${IMAGE}:${{ steps.semver.outputs.minor }}"
+          docker tag "${IMAGE}:${{ steps.semver.outputs.full }}" "${IMAGE}:${{ steps.semver.outputs.major }}"
+          docker tag "${IMAGE}:${{ steps.semver.outputs.full }}" "${IMAGE}:latest"
           echo "IMAGE=${IMAGE}" >> "$GITHUB_ENV"
 
       - name: Push to registry
         run: |
-          buildah login -u "${{ github.repository_owner }}" \
-            -p "${{ secrets.REGISTRY_TOKEN }}" \
-            "${IMAGE%%/*}"
-          buildah push "${IMAGE}:${{ steps.semver.outputs.full }}"
-          buildah push "${IMAGE}:${{ steps.semver.outputs.minor }}"
-          buildah push "${IMAGE}:${{ steps.semver.outputs.major }}"
-          buildah push "${IMAGE}:latest"
+          echo "${{ secrets.REGISTRY_TOKEN }}" | docker login -u "${{ github.repository_owner }}" --password-stdin "${IMAGE%%/*}"
+          docker push "${IMAGE}:${{ steps.semver.outputs.full }}"
+          docker push "${IMAGE}:${{ steps.semver.outputs.minor }}"
+          docker push "${IMAGE}:${{ steps.semver.outputs.major }}"
+          docker push "${IMAGE}:latest"