feat(search): add DisambiguationPicker single-select disclosure (#739)

Accessible disclosure: aria-expanded/aria-controls trigger, focus moves
into the option list on open, Escape and click-outside close and return
focus to the trigger, selecting a candidate emits onSelect. Single-select
(GET re-run) per the resolved #738 open decision — backend has no
multi-sender OR param. 5 vitest-browser-svelte specs.

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

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

@@ -0,0 +1,71 @@
+import { describe, expect, it, vi, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import DisambiguationPicker from './DisambiguationPicker.svelte';
+import type { components } from '$lib/generated/api';
+
+type PersonHint = components['schemas']['PersonHint'];
+
+afterEach(() => cleanup());
+
+const persons: PersonHint[] = [
+	{ id: 'w1', displayName: 'Walter Raddatz' },
+	{ id: 'w2', displayName: 'Walter Müller' }
+];
+
+function pressEscape() {
+	(document.activeElement as HTMLElement).dispatchEvent(
+		new KeyboardEvent('keydown', { key: 'Escape', bubbles: true })
+	);
+}
+
+describe('DisambiguationPicker', () => {
+	it('opens the picker and shows a select option per ambiguous person', async () => {
+		render(DisambiguationPicker, { persons, onSelect: vi.fn() });
+		await page.getByRole('button', { name: /Mehrere Personen gefunden/ }).click();
+		await expect
+			.element(page.getByRole('button', { name: 'Walter Raddatz auswählen' }))
+			.toBeInTheDocument();
+		await expect
+			.element(page.getByRole('button', { name: 'Walter Müller auswählen' }))
+			.toBeInTheDocument();
+	});
+
+	it('moves focus into the picker list on open', async () => {
+		render(DisambiguationPicker, { persons, onSelect: vi.fn() });
+		await page.getByRole('button', { name: /Mehrere Personen gefunden/ }).click();
+		await expect
+			.element(page.getByRole('button', { name: 'Walter Raddatz auswählen' }))
+			.toHaveFocus();
+	});
+
+	it('returns focus to the trigger when closed with Escape', async () => {
+		render(DisambiguationPicker, { persons, onSelect: vi.fn() });
+		const trigger = page.getByRole('button', { name: /Mehrere Personen gefunden/ });
+		await trigger.click();
+		await expect
+			.element(page.getByRole('button', { name: 'Walter Raddatz auswählen' }))
+			.toHaveFocus();
+		pressEscape();
+		await expect.element(trigger).toHaveFocus();
+	});
+
+	it('does not call onSelect when dismissed without choosing', async () => {
+		const onSelect = vi.fn();
+		render(DisambiguationPicker, { persons, onSelect });
+		await page.getByRole('button', { name: /Mehrere Personen gefunden/ }).click();
+		await expect
+			.element(page.getByRole('button', { name: 'Walter Raddatz auswählen' }))
+			.toHaveFocus();
+		pressEscape();
+		expect(onSelect).not.toHaveBeenCalled();
+	});
+
+	it('calls onSelect with the chosen person', async () => {
+		const onSelect = vi.fn();
+		render(DisambiguationPicker, { persons, onSelect });
+		await page.getByRole('button', { name: /Mehrere Personen gefunden/ }).click();
+		await page.getByRole('button', { name: 'Walter Müller auswählen' }).click();
+		expect(onSelect).toHaveBeenCalledWith(persons[1]);
+	});
+});