test(admin): expand admin/groups/[id] page coverage

Adds banner-hidden defaults, all-8-permission-checkboxes count,
empty permissions array.

4 new tests covering ~6 branches.

Refs #496.

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

frontend/src/routes/admin/groups/[id]/page.svelte.test.ts

@@ -87,4 +87,39 @@ describe('admin/groups/[id] page', () => {
 		await expect.element(page.getByRole('button', { name: /löschen/i })).toBeVisible();
 		await expect.element(page.getByRole('button', { name: /speichern/i })).toBeVisible();
 	});
+
+	it('does not render success banner when form is undefined', async () => {
+		render(AdminGroupEditPage, { props: { data: { group: baseGroup() }, form: undefined } });
+
+		const banner = document.querySelector('.bg-green-50');
+		expect(banner).toBeNull();
+	});
+
+	it('does not render error-banner div when form.success is true (success path only)', async () => {
+		render(AdminGroupEditPage, {
+			props: { data: { group: baseGroup() }, form: { success: true } }
+		});
+
+		// Error banner is the <div> with bg-red-50 — the delete button is also red but is a button
+		const errorBanner = document.querySelector('div.bg-red-50');
+		expect(errorBanner).toBeNull();
+	});
+
+	it('renders all 8 permission checkboxes (4 standard + 4 admin)', async () => {
+		render(AdminGroupEditPage, { props: { data: { group: baseGroup() }, form: undefined } });
+
+		const checkboxes = document.querySelectorAll('input[name="permissions"]');
+		expect(checkboxes.length).toBe(8);
+	});
+
+	it('handles a group with empty permissions array', async () => {
+		render(AdminGroupEditPage, {
+			props: { data: { group: baseGroup({ permissions: [] }) }, form: undefined }
+		});
+
+		const checkboxes = Array.from(
+			document.querySelectorAll('input[name="permissions"]')
+		) as HTMLInputElement[];
+		expect(checkboxes.every((c) => !c.checked)).toBe(true);
+	});
 });