feat(registry-cache): add Docker Hub pull-through cache + dind mirror config

Deploy registry:2 as Docker Hub pull-through cache on chemavx-k8 (hostPort 5000,
ClusterIP 10.43.163.56:5000). Configures dind runner to use local mirror via
daemon.json to eliminate Docker Hub rate limit failures in CI/CD.

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

registry-cache/service-registry-cache.yaml

@@ -0,0 +1,13 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: registry-cache
+  namespace: registry-cache
+spec:
+  selector:
+    app: registry-cache
+  ports:
+  - port: 5000
+    targetPort: 5000
+    protocol: TCP
+  type: ClusterIP