fix(invites): resolve svelte-check warnings in UserGroupsSection and page.server.test

Use untrack() for intentional one-time prop seed in UserGroupsSection.
Add explicit LoadData type alias in page.server.test to avoid void|Record<string,any> union.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/user/UserGroupsSection.svelte

@@ -1,4 +1,5 @@
 <script lang="ts">
+import { untrack } from 'svelte';
 import { m } from '$lib/paraglide/messages.js';
 
 let {
@@ -9,7 +10,7 @@ let {
 	selectedGroupIds?: string[];
 } = $props();
 
-let selected = $state<string[]>([...selectedGroupIds]);
+let selected = $state<string[]>(untrack(() => [...selectedGroupIds]));
 </script>
 
 <fieldset class="flex flex-wrap gap-3 border-none p-0">

frontend/src/routes/admin/invites/page.server.test.ts

@@ -5,6 +5,17 @@ vi.mock('$env/dynamic/private', () => ({
 }));
 
 import { load, actions } from './+page.server';
+import type { UserGroup } from './+page.server';
+
+// PageServerLoad annotates the return as `void | (...)`. This explicit shape avoids
+// the void and the Record<string, any> from the generic constraint.
+type LoadData = {
+	invites: unknown[];
+	status: string;
+	loadError: string | null;
+	groups: UserGroup[];
+	groupsLoadError: string | null;
+};
 
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
 type AnyFetch = (...args: any[]) => any;
@@ -40,7 +51,7 @@ describe('admin/invites load()', () => {
 			])
 		);
 
-		const result = await load(event());
+		const result = (await load(event())) as LoadData;
 
 		expect(result.groups).toHaveLength(2);
 		expect(result.groupsLoadError).toBeNull();
@@ -55,7 +66,7 @@ describe('admin/invites load()', () => {
 			])
 		);
 
-		const result = await load(event());
+		const result = (await load(event())) as LoadData;
 
 		expect(result.groups.map((g) => g.name)).toEqual(['Alfa', 'Mitte', 'Zebra']);
 	});
@@ -65,7 +76,7 @@ describe('admin/invites load()', () => {
 			.mockResolvedValueOnce(mockResponse(true, []))
 			.mockResolvedValueOnce(mockResponse(false, { code: 'FORBIDDEN' }, 403));
 
-		const result = await load(event());
+		const result = (await load(event())) as LoadData;
 
 		expect(result.groups).toEqual([]);
 		expect(result.groupsLoadError).toBe('FORBIDDEN');
@@ -76,7 +87,7 @@ describe('admin/invites load()', () => {
 			.mockResolvedValueOnce(mockResponse(true, []))
 			.mockResolvedValueOnce(mockResponse(false, null, 500));
 
-		const result = await load(event());
+		const result = (await load(event())) as LoadData;
 
 		expect(result.groupsLoadError).toBe('INTERNAL_ERROR');
 	});