fix: use docker login CLI instead of login-action for Gitea compat

docker/login-action@v3 fails with 'Username and password required' on
Gitea Actions — secrets not passed to action with: inputs. Switch to
direct docker login CLI which reliably interpolates secrets in run: steps.

.gitea/workflows/build-push.yaml

@@ -125,18 +125,11 @@ jobs:
         uses: docker/setup-buildx-action@v3
 
       - name: Login to Gitea Registry
-        uses: docker/login-action@v3
-        with:
-          registry: ${{ env.REGISTRY_HOST }}
-          username: ${{ secrets.REGISTRY_USER }}
-          password: ${{ secrets.REGISTRY_TOKEN }}
+        run: echo "${{ secrets.REGISTRY_TOKEN }}" | docker login "${{ env.REGISTRY_HOST }}" -u "${{ secrets.REGISTRY_USER }}" --password-stdin
 
       - name: Login to Docker Hub
         if: vars.DOCKERHUB_USERNAME != ''
-        uses: docker/login-action@v3
-        with:
-          username: ${{ vars.DOCKERHUB_USERNAME }}
-          password: ${{ secrets.DOCKERHUB_TOKEN }}
+        run: echo "${{ secrets.DOCKERHUB_TOKEN }}" | docker login -u "${{ vars.DOCKERHUB_USERNAME }}" --password-stdin
 
       - name: Extract metadata
         id: meta