ci: switch from legacy docker build to buildx

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -36,7 +36,7 @@ jobs:
     steps:
       - name: Clone repository
         run: |
-          apk add --no-cache git curl docker-cli
+          apk add --no-cache git curl docker-cli docker-cli-buildx
           git clone https://${{ secrets.GITEA_TOKEN }}@gitea.jeanlucmakiola.de/${{ gitea.repository }}.git repo
           cd repo
           git checkout Develop
@@ -46,7 +46,7 @@ jobs:
         run: |
           REGISTRY="gitea.jeanlucmakiola.de"
           IMAGE="${REGISTRY}/${{ gitea.repository_owner }}/gearbox"
-          docker build -t "${IMAGE}:develop" .
+          docker buildx build -t "${IMAGE}:develop" .
           echo "${{ secrets.REGISTRY_TOKEN }}" | docker login "$REGISTRY" -u "${{ gitea.repository_owner }}" --password-stdin
           docker push "${IMAGE}:develop"