fix(e2e): fix 4 failing e2e tests — strict mode locator and nested form

documents.spec.ts: replace getByText with getByRole('heading') to avoid
Svelte's #svelte-announcer matching the same text (strict mode violation).

SaveBar.svelte: move <form id="mark-for-review-form"> out of the component
and into +page.svelte as a sibling of delete-form. The form was previously
nested inside <form id="update-form">, which is invalid HTML. The browser
auto-repaired it, causing a Svelte hydration mismatch that broke the edit
form's use:enhance, preventing version snapshots from being recorded —
leaving history tests with 0 versions instead of the expected 2.

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

frontend/e2e/documents.spec.ts

@@ -167,7 +167,7 @@ test.describe('Document editing', () => {
 		await page.getByRole('button', { name: 'Speichern', exact: true }).click();
 
 		await expect(page).toHaveURL(/\/documents\/[^/]+$/);
-		await expect(page.getByText('E2E Testbrief (überarbeitet)')).toBeVisible();
+		await expect(page.getByRole('heading', { name: 'E2E Testbrief (überarbeitet)' })).toBeVisible();
 		await page.screenshot({ path: 'test-results/e2e/document-edit-save.png' });
 	});
 });