fix(ui): disable Add Monitor button when no eligible systems exist (#2392)

internal/site/src/components/network-monitors-table/monitor-dialog.tsx

@@ -353,6 +353,8 @@ export function AddMonitorDialog({ systemId, monitors }: { systemId?: string; mo
 	const bulkFormRef = useRef<HTMLFormElement>(null)
 	const { toast } = useToast()
 	const { t } = useLingui()
+	const systems = useStore($systems)
+	const hasEligibleSystems = systemId ? true : systems.some(supportsNetworkMonitors)
 
 	const resetBulkForm = () => {
 		setBulkInput("")
@@ -443,14 +445,19 @@ export function AddMonitorDialog({ systemId, monitors }: { systemId?: string; mo
 	return (
 		<>
 			<div className="flex gap-0 rounded-lg">
-				<Button variant="outline" onClick={openAdd} className="rounded-e-none grow">
+				<Button variant="outline" onClick={openAdd} className="rounded-e-none grow" disabled={!hasEligibleSystems}>
 					{/* <PlusIcon className="size-4 me-1" /> */}
 					<Trans>Add {{ foo: t`Monitor` }}</Trans>
 				</Button>
 				<div className="w-px h-full bg-muted"></div>
 				<DropdownMenu>
 					<DropdownMenuTrigger asChild>
-						<Button variant="outline" className="px-2 rounded-s-none border-s-0" aria-label={`More actions`}>
+						<Button
+							variant="outline"
+							className="px-2 rounded-s-none border-s-0"
+							aria-label={`More actions`}
+							disabled={!hasEligibleSystems}
+						>
 							<ChevronDownIcon className="size-4" />
 						</Button>
 					</DropdownMenuTrigger>