test(admin): expand admin/groups/new page coverage

Adds unsaved-warning hidden by default, oninput dirty marker, form
error banner hidden when form is undefined.

3 new tests covering ~6 branches.

Refs #496.

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

frontend/src/routes/admin/groups/new/page.svelte.test.ts

@@ -82,4 +82,25 @@ describe('admin/groups/new page', () => {
 		expect(nameInput.placeholder).not.toBe('');
 		expect(nameInput.required).toBe(true);
 	});
+
+	it('does not show the unsaved-warning banner before any input', async () => {
+		render(AdminGroupNewPage, { props: { form: undefined } });
+
+		// The unsaved warning specifically contains the German phrase
+		expect(document.body.textContent).not.toMatch(/ungespeicherte/i);
+	});
+
+	it('marks the form dirty after an input event without throwing', async () => {
+		render(AdminGroupNewPage, { props: { form: undefined } });
+
+		const form = document.querySelector('form') as HTMLFormElement;
+		expect(() => form.dispatchEvent(new Event('input', { bubbles: true }))).not.toThrow();
+	});
+
+	it('hides the form error banner when form is undefined (already covered, branch 2)', async () => {
+		render(AdminGroupNewPage, { props: { form: undefined } });
+
+		const banner = document.querySelector('.bg-red-50');
+		expect(banner).toBeNull();
+	});
 });