fix: use docker/login-action for both registries to fix buildx auth

- Docker Hub login now happens before Gitea login, both via login-action
- Previous manual config.json write was clobbering Docker Hub auth
- buildx docker-container driver inherits auth from login-action correctly
- Fixes 429 Too Many Requests from unauthenticated Docker Hub pulls

.gitea/workflows/ci.yml

@@ -91,13 +91,6 @@ jobs:
               http = true
               insecure = true
 
-      - name: Login to Docker Hub
-        if: vars.DOCKERHUB_USERNAME != ''
-        uses: docker/login-action@v3
-        with:
-          username: ${{ vars.DOCKERHUB_USERNAME }}
-          password: ${{ secrets.DOCKERHUB_TOKEN }}
-
       - name: Configure Docker for insecure registry
         run: |
           sudo mkdir -p /etc/docker
@@ -105,20 +98,19 @@ jobs:
           sudo systemctl restart docker || sudo service docker restart || true
           sleep 2
 
+      - name: Login to Docker Hub
+        if: vars.DOCKERHUB_USERNAME != ''
+        uses: docker/login-action@v3
+        with:
+          username: ${{ vars.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
       - name: Login to Gitea Registry
-        run: |
-          AUTH=$(echo -n "${{ secrets.REGISTRY_USER }}:${{ secrets.REGISTRY_TOKEN }}" | base64 -w0)
-          mkdir -p ~/.docker
-          cat > ~/.docker/config.json << EOF
-          {
-            "auths": {
-              "${{ env.REGISTRY_HOST }}": {
-                "auth": "$AUTH"
-              }
-            }
-          }
-          EOF
-          echo "Auth configured for ${{ env.REGISTRY_HOST }}"
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY_HOST }}
+          username: ${{ secrets.REGISTRY_USER }}
+          password: ${{ secrets.REGISTRY_TOKEN }}
 
       - name: Extract metadata
         id: meta