fix: use docker build --push (buildx driver skips local store)

Runner uses buildx with docker-container driver which doesn't
populate the local image store. --push builds and pushes directly.

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

.gitea/workflows/ci.yaml

@@ -40,5 +40,4 @@ jobs:
         env:
           HARBOR_USER: ${{ secrets.HARBOR_USER }}
           HARBOR_PASS: ${{ secrets.HARBOR_PASS }}
-      - run: docker build -t harbor.mymx.me/s5p/s5p:latest -f Containerfile .
-      - run: docker push harbor.mymx.me/s5p/s5p:latest
+      - run: docker build --push -t harbor.mymx.me/s5p/s5p:latest -f Containerfile .