chore(k8s): take the image reference from build-tools

deploy substitutes ${IMAGE} with <registry>/<owner>/<name>:<tag> from the build-tools config, so the registry is set in one place (infra) instead of in every manifest. Renders the same reference as before. Same change as shiny/time-service#864.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

k8s/deploy.yaml

@@ -13,7 +13,7 @@ spec:
         spec:
           containers:
             - name: dancefetcher
-              image: oci.unbound.se/dancefinder/dancefetcher:${COMMIT}
+              image: ${IMAGE}
               imagePullPolicy: Always
               resources:
                 limits: