fix(search): derive disambiguation trigger aria-label from match count (#763 review)

The trigger hardcoded the multiple-people label for every count, so a
single did-you-mean picker announced "Mehrere Personen gefunden" to
screen readers while sighted users saw one name and a "Meintest du …?"
heading. Derive the trigger's accessible name from persons.length: a
single suggestion reuses the heading prop, two or more keep the
multiple-people label. Visible truncated name span unchanged.

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

frontend/src/routes/search/DisambiguationPicker.svelte.spec.ts

@@ -78,7 +78,7 @@ describe('DisambiguationPicker', () => {
 			showCue: false,
 			onSelect: vi.fn()
 		});
-		await page.getByRole('button', { name: /Mehrere Personen gefunden/ }).click();
+		await page.getByRole('button', { name: 'Meintest du Clara Cramer?' }).click();
 		await expect.element(page.getByText('Meintest du Clara Cramer?')).toBeVisible();
 	});
 
@@ -96,4 +96,23 @@ describe('DisambiguationPicker', () => {
 		render(DisambiguationPicker, { ...multiProps, onSelect: vi.fn() });
 		await expect.element(page.getByText('(auswählen…)')).toBeVisible();
 	});
+
+	it('announces the did-you-mean heading as the trigger accessible name for a single suggestion', async () => {
+		render(DisambiguationPicker, {
+			persons: [{ id: 'c1', displayName: 'Clara Cramer' }],
+			heading: 'Meintest du Clara Cramer?',
+			showCue: false,
+			onSelect: vi.fn()
+		});
+		await expect
+			.element(page.getByRole('button', { name: 'Meintest du Clara Cramer?' }))
+			.toBeInTheDocument();
+	});
+
+	it('keeps the multiple-people trigger accessible name for two or more suggestions', async () => {
+		render(DisambiguationPicker, { ...multiProps, onSelect: vi.fn() });
+		await expect
+			.element(page.getByRole('button', { name: /Mehrere Personen gefunden/ }))
+			.toBeInTheDocument();
+	});
 });