Fix: WidgetConfigDialog scope + reorder race condition

Two bugs in the widget config dialog:

1. Service Overview edit showed main-dashboard widgets. The dialog
   called useWidgetInstances() with no args, fetching ALL widgets. Now
   accepts a serviceId prop; OverviewTab passes instance.id so the
   dialog lists + creates only service-scoped widgets. New built-in
   widgets added from a service Overview inherit the serviceId.

2. Reorder up/down buttons did nothing. moveInstance fired two
   saveWidget mutations via Promise.all — the first mutation's
   onSuccess cache invalidation triggered a refetch before the second
   completed, reverting the swap. Changed to sequential awaits so
   both sort_order writes land before the cache refreshes.

127 tests pass; lint/build green.

frontend/src/components/WidgetConfigDialog.tsx

@@ -38,6 +38,8 @@ import {
 interface Props {
 	open: boolean;
 	onClose: () => void;
+	/** When set, scope the dialog to a specific service instance's widgets. */
+	serviceId?: string;
 }
 
 interface Draft {
@@ -164,8 +166,8 @@ function WidgetConfigEditor({
 	);
 }
 
-export function WidgetConfigDialog({ open, onClose }: Props) {
-	const { data: instances = [] } = useWidgetInstances();
+export function WidgetConfigDialog({ open, onClose, serviceId }: Props) {
+	const { data: instances = [] } = useWidgetInstances(serviceId);
 	const { data: services = [] } = useServiceInstances();
 	const { data: tasks = [] } = useTasks();
 	const saveWidget = useSaveWidgetInstance();
@@ -184,7 +186,7 @@ export function WidgetConfigDialog({ open, onClose }: Props) {
 	function startAddBuiltIn(kind: string) {
 		const binding = BUILTIN_WIDGETS[kind];
 		setDraft({
-			serviceId: null,
+			serviceId: serviceId ?? null,
 			widgetKind: kind,
 			title: binding?.name ?? kind,
 			config: { ...(binding?.defaultConfig ?? {}) },
@@ -255,10 +257,10 @@ export function WidgetConfigDialog({ open, onClose }: Props) {
 		if (targetIndex < 0 || targetIndex >= sortedInstances.length) return;
 		const a = sortedInstances[index];
 		const b = sortedInstances[targetIndex];
-		await Promise.all([
-			saveWidget.mutateAsync({ ...a, sort_order: b.sort_order }),
-			saveWidget.mutateAsync({ ...b, sort_order: a.sort_order }),
-		]);
+		// Sequential (not Promise.all) to avoid a race where the first mutation's
+		// cache invalidation refetches before the second completes, reverting the swap.
+		await saveWidget.mutateAsync({ ...a, sort_order: b.sort_order });
+		await saveWidget.mutateAsync({ ...b, sort_order: a.sort_order });
 	}
 
 	async function removeInstance(instance: WidgetInstance) {

frontend/src/pages/service-tabs/OverviewTab.tsx

@@ -72,6 +72,7 @@ export function OverviewTab({ instance }: { instance: ServiceInstance }) {
 			<WidgetConfigDialog
 				open={configOpen}
 				onClose={() => setConfigOpen(false)}
+				serviceId={instance.id}
 			/>
 		</div>
 	);