feat: K8s集群导出改为导出所有命名空间资源，去掉命名空间选择

- 后端: 新增 ExportResourcesAllNS handler (GET /:clusterCode/export)，遍历所有NS收集资源
- 前端: KubernetesClusters 导出弹窗去掉命名空间输入框，一键导出全部NS
- API: exportResources → exportAllResources，无需传 namespace 参数

frontend/src/components/kubernetes/KubernetesClusters.tsx

@@ -52,7 +52,6 @@ export function KubernetesClusters() {
 
   // 导出资源弹窗
   const [exportCluster, setExportCluster] = useState<any>(null);
-  const [exportNs, setExportNs] = useState('default');
   const [exporting, setExporting] = useState(false);
 
   const loadData = async () => {
@@ -113,11 +112,10 @@ export function KubernetesClusters() {
   const handleExport = async () => {
     if (!exportCluster) return;
     const code = exportCluster.code || String(exportCluster.id);
-    if (!exportNs.trim()) { toast.error('请输入命名空间'); return; }
     try {
       setExporting(true);
-      toast.info(`正在导出 ${exportNs} 命名空间的资源...`);
-      await kubernetesApi.exportResources(code, exportNs.trim());
+      toast.info(`正在导出 ${exportCluster.name} 所有命名空间的资源...`);
+      await kubernetesApi.exportAllResources(code);
       toast.success('导出完成，已开始下载');
       setExportCluster(null);
     } catch (e: any) {
@@ -359,7 +357,6 @@ export function KubernetesClusters() {
                             onClick={(e) => {
                               e.stopPropagation();
                               setExportCluster(cluster);
-                              setExportNs('default');
                             }}
                           >
                             <Download className="h-4 w-4 mr-2" />
@@ -473,16 +470,8 @@ export function KubernetesClusters() {
           <div className="bg-slate-900 border border-slate-700 rounded-lg p-5 w-96 shadow-xl" onClick={(e) => e.stopPropagation()}>
             <h3 className="text-base font-semibold text-slate-100 mb-1">导出集群资源</h3>
             <p className="text-xs text-slate-400 mb-4">
-              导出 {exportCluster.name} 的 Deployment + Service + Ingress + ConfigMap + Secret 为 tar.gz
+              导出 {exportCluster.name} 所有命名空间的 Deployment、Service、Ingress、ConfigMap、Secret 为 tar.gz
             </p>
-            <label className="text-xs text-slate-300 mb-1.5 block">命名空间</label>
-            <Input
-              value={exportNs}
-              onChange={(e) => setExportNs(e.target.value)}
-              placeholder="default"
-              className="bg-slate-800 border-slate-700 text-slate-100 mb-4"
-              onKeyDown={(e) => e.key === 'Enter' && handleExport()}
-            />
             <div className="flex justify-end gap-2">
               <Button variant="outline" className="border-slate-700 text-slate-300" onClick={() => setExportCluster(null)}>取消</Button>
               <Button className="bg-blue-600 hover:bg-blue-700 text-white" onClick={handleExport} disabled={exporting}>