test(transcription): assert error banner shows domain-specific message

Adds toHaveTextContent(m.transcription_mark_all_reviewed_error()) to the
error-present test. The previous check only asserted presence via
role="alert", which would not have caught the dead key bug — the banner
was showing the generic fallback rather than the operation-specific copy.

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

frontend/src/lib/document/transcription/TranscriptionEditView.svelte.spec.ts

@@ -381,6 +381,9 @@ describe('TranscriptionEditView — mark all reviewed', () => {
 		btnEl.dispatchEvent(new MouseEvent('click', { bubbles: true, cancelable: true }));
 
 		await expect.element(page.getByRole('alert')).toBeInTheDocument();
+		await expect
+			.element(page.getByRole('alert'))
+			.toHaveTextContent(m.transcription_mark_all_reviewed_error());
 	});
 
 	it('clears error when dismiss button is clicked', async () => {