test(timeline): assert submit-disabled transition and ≥44px chip targets

Tighten the review-flagged test gaps (no production change):
- submitting state: the old test only asserted the button was initially
  enabled (a tautology). Now stub a never-resolving fetch, click Speichern, and
  assert the button gains `disabled` — exercising the double-submit guard
  (Decision 8).
- the two redirect-throwing save tests now use `await expect(...).rejects` so a
  future missing redirect fails loudly instead of being swallowed by try/catch.
- the YEAR end-date-hide assertion uses getByLabelText('Enddatum') not-present,
  symmetric with the RANGE reveal, instead of a raw #eventDateEnd querySelector.
- PersonMultiSelect + DocumentMultiSelect: assert the chip remove button carries
  the min-h-[44px]/min-w-[44px] target the rtm cites for REQ-017.

Addresses PR #832 review (Tester + Requirements Engineer test-coverage concerns).

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

frontend/src/lib/timeline/EventForm.svelte.spec.ts

@@ -1,10 +1,13 @@
-import { afterEach, describe, expect, it } from 'vitest';
+import { afterEach, describe, expect, it, vi } from 'vitest';
 import { cleanup, render } from 'vitest-browser-svelte';
 import { page } from 'vitest/browser';
 import EventForm from './EventForm.svelte';
 import type { components } from '$lib/generated/api';
 
-afterEach(() => cleanup());
+afterEach(() => {
+	cleanup();
+	vi.unstubAllGlobals();
+});
 
 type TimelineEventView = components['schemas']['TimelineEventView'];
 
@@ -39,7 +42,7 @@ describe('EventForm — date precision RANGE reveal (headline AC, REQ-008/009)',
 	it('hides the end-date field when precision is YEAR', async () => {
 		render(EventForm, { event: makeEvent({ precision: 'YEAR' }) });
 		await expect.element(page.getByTestId('end-date-region')).toBeInTheDocument();
-		expect(document.querySelector('#eventDateEnd')).toBeNull();
+		await expect.element(page.getByLabelText('Enddatum')).not.toBeInTheDocument();
 	});
 });
 
@@ -82,11 +85,20 @@ describe('EventForm — server date error wired per-field (REQ-011)', () => {
 	});
 });
 
-describe('EventForm — submitting state (named AC)', () => {
-	it('renders an enabled submit button initially', async () => {
+describe('EventForm — submitting state (named AC, Decision 8)', () => {
+	it('disables the submit button while submitting', async () => {
+		// A never-resolving fetch keeps use:enhance in flight so the disabled
+		// transition (the double-submit guard) is observable rather than racing the
+		// reset in the result callback.
+		vi.stubGlobal(
+			'fetch',
+			vi.fn(() => new Promise(() => {}))
+		);
 		render(EventForm, { event: makeEvent() });
 		const btn = page.getByRole('button', { name: 'Speichern' });
 		await expect.element(btn).not.toBeDisabled();
+		await btn.click();
+		await expect.element(btn).toBeDisabled();
 	});
 });