feat: add LoadingOverlay component with contextual busy messages for async operations across cluster sync, firewall preview/apply, IPAM discovery/export, node agent installer, and policy compilation

Add LoadingOverlay component with spinner, customizable title/message, and backdrop blur styling, implement busy state tracking with setBusyMessage in Clusters/FirewallPreview/Ipam/Nodes/Policies pages, wrap async operations (cluster test/sync, firewall preview/apply, IPAM discover/export CSV, node agent installer

frontend/src/pages/Ipam.tsx

@@ -5,6 +5,7 @@ import { Database, Download, Plus } from "lucide-react";
 import { api, authorizedFetch, IpAddress, Network, Subnet } from "../api/client";
 import { DataTable } from "../components/DataTable";
 import { buttonClass, Field, inputClass, secondaryButtonClass, selectClass } from "../components/FormControls";
+import { LoadingOverlay } from "../components/LoadingOverlay";
 import { Modal } from "../components/Modal";
 import { PageHeader } from "../components/PageHeader";
 
@@ -18,6 +19,7 @@ export function Ipam() {
   const [ipForm, setIpForm] = useState({ subnet_id: "", address: "10.50.0.20", status: "reserved", note: "" });
   const [subnetOpen, setSubnetOpen] = useState(false);
   const [ipOpen, setIpOpen] = useState(false);
+  const [busyMessage, setBusyMessage] = useState("");
 
   const createSubnet = useMutation({
     mutationFn: () => api<Subnet>("/ipam/subnets", { method: "POST", body: JSON.stringify({ ...subnetForm, network_id: subnetForm.network_id || networks.data?.[0]?.id }) }),
@@ -49,17 +51,23 @@ export function Ipam() {
   }
 
   async function exportCsv() {
-    const response = await authorizedFetch("/ipam/export.csv");
-    const blob = await response.blob();
-    const url = URL.createObjectURL(blob);
-    const link = document.createElement("a");
-    link.href = url;
-    link.download = "nexafabric-ipam.csv";
-    link.click();
-    URL.revokeObjectURL(url);
+    setBusyMessage("Preparing IPAM export...");
+    try {
+      const response = await authorizedFetch("/ipam/export.csv");
+      const blob = await response.blob();
+      const url = URL.createObjectURL(blob);
+      const link = document.createElement("a");
+      link.href = url;
+      link.download = "nexafabric-ipam.csv";
+      link.click();
+      URL.revokeObjectURL(url);
+    } finally {
+      setBusyMessage("");
+    }
   }
 
   async function discoverIpam() {
+    setBusyMessage("Discovering IP addresses from Proxmox...");
     try {
       const result = await api<{ imported: number; removed: number; errors: Array<Record<string, unknown>> }>("/ipam/discover", { method: "POST" });
       setMessage(`Discovery imported ${result.imported} IP addresses and removed ${result.removed} container bridge entries${result.errors.length ? " with errors" : ""}.`);
@@ -67,12 +75,15 @@ export function Ipam() {
       await queryClient.invalidateQueries({ queryKey: ["addresses"] });
     } catch (error) {
       setMessage(error instanceof Error ? error.message : "IPAM discovery failed.");
+    } finally {
+      setBusyMessage("");
     }
   }
 
   return (
     <>
       <PageHeader title="IPAM" subtitle="Manage subnets, reservations, assignments, conflicts, and export state." />
+      <LoadingOverlay open={Boolean(busyMessage)} message={busyMessage} />
       <div className="space-y-4">
         <div className="flex flex-wrap gap-2">
           <button className={buttonClass} onClick={() => setSubnetOpen(true)}><Plus size={16} /> Add Subnet</button>