test(stammbaum): cover animateView rAF tween + server 401/500 paths (#692)

Add a deterministic stubbed-rAF test for animateView's animated path (was only
covering the reduced-motion branch) and assert the server load redirects on 401
and throws on a network 500 (QA review).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/routes/stammbaum/page.server.test.ts

@@ -16,6 +16,12 @@ function mockNetwork() {
 	} as unknown as ReturnType<typeof createApiClient>);
 }
 
+function mockNetworkResponse(status: number) {
+	vi.mocked(createApiClient).mockReturnValue({
+		GET: vi.fn().mockResolvedValue({ response: { ok: false, status }, error: { code: 'X' } })
+	} as unknown as ReturnType<typeof createApiClient>);
+}
+
 function loadEvent(query = '') {
 	const url = new URL(`http://localhost/stammbaum${query}`);
 	return {
@@ -53,4 +59,19 @@ describe('/stammbaum +page.server load — initialView', () => {
 		const result = await load(loadEvent('?z=99') as never);
 		expect(result.initialView.z).toBe(MAX_ZOOM);
 	});
+
+	it('redirects to /login when the network API returns 401', async () => {
+		mockNetworkResponse(401);
+		const { load } = await import('./+page.server');
+		await expect(load(loadEvent() as never)).rejects.toMatchObject({
+			status: 302,
+			location: '/login'
+		});
+	});
+
+	it('throws an HTTP error when the network API fails', async () => {
+		mockNetworkResponse(500);
+		const { load } = await import('./+page.server');
+		await expect(load(loadEvent() as never)).rejects.toMatchObject({ status: 500 });
+	});
 });