Fix CI: use REGISTRY_TOKEN secret for registry auth

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitea/workflows/build.yml

@@ -20,8 +20,8 @@ jobs:
         uses: docker/login-action@v3
         with:
           registry: ${{ env.REGISTRY }}
-          username: ${{ secrets.REGISTRY_USER }}
-          password: ${{ secrets.REGISTRY_PASSWORD }}
+          username: matt
+          password: ${{ secrets.REGISTRY_TOKEN }}
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3