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>

argocd/application-registry-cache.yaml

@@ -0,0 +1,20 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: registry-cache
+  namespace: argocd
+spec:
+  project: default
+  source:
+    repoURL: http://gitea.gitea.svc.cluster.local:3000/chemavx/k8s-manifests.git
+    targetRevision: main
+    path: registry-cache
+  destination:
+    server: https://kubernetes.default.svc
+    namespace: registry-cache
+  syncPolicy:
+    automated:
+      prune: true
+      selfHeal: true
+    syncOptions:
+      - CreateNamespace=true