fix(k8s): YAML 弹框 Portal 到 body 修复居中偏移

PageTransition 的 transform 会使 fixed 弹框相对页面定位而非视口，
YamlViewer 尺寸较大时容易跑出可视区。统一用 ModalOverlay Portal。

frontend/src/components/kubernetes/YamlImportDialog.tsx

@@ -2,6 +2,7 @@
 import { useState } from 'react';
 import { X, Upload, Loader2 } from 'lucide-react';
 import { Button } from '@/components/ui/button';
+import { ModalOverlay } from '@/components/ui/modal-overlay';
 import { useToast } from '@/hooks/use-toast';
 import { kubernetesApi } from '@/api';
 import CodeMirror from '@uiw/react-codemirror';
@@ -36,7 +37,7 @@ export function YamlImportDialog({ clusterCode, onClose, onApplied }: YamlImport
   };
 
   return (
-    <div className="fixed inset-0 z-50 flex items-center justify-center bg-black/60" onClick={onClose}>
+    <ModalOverlay onClose={onClose}>
       <div
         className="bg-[var(--dg-bg-primary)] border border-[var(--dg-border)] rounded-xl w-[92vw] max-w-4xl max-h-[85vh] flex flex-col shadow-2xl"
         onClick={(e) => e.stopPropagation()}
@@ -71,6 +72,6 @@ export function YamlImportDialog({ clusterCode, onClose, onApplied }: YamlImport
           </Button>
         </div>
       </div>
-    </div>
+    </ModalOverlay>
   );
 }