feat(shared-ui,shared-stores): add FavoriteButton component and toggleField utility

FavoriteButton: reusable heart/star/pin toggle with filled/outline states,
accessible labels, configurable colors. toggleField: generic boolean field
toggle for Dexie records (isFavorite, isPinned, etc.) with timestamp.
Includes 11 tests (6 FavoriteButton + 5 toggleField).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/shared-ui/src/molecules/FavoriteButton.test.ts

@@ -0,0 +1,47 @@
+import { describe, it, expect, vi } from 'vitest';
+import { render, screen, fireEvent } from '@testing-library/svelte';
+import FavoriteButton from './FavoriteButton.svelte';
+
+describe('FavoriteButton', () => {
+	it('renders with heart icon by default', () => {
+		const { container } = render(FavoriteButton, {
+			props: { active: false, onclick: vi.fn() },
+		});
+		expect(container.querySelector('button')).toBeInTheDocument();
+	});
+
+	it('has correct aria-label when inactive', () => {
+		render(FavoriteButton, {
+			props: { active: false, onclick: vi.fn() },
+		});
+		expect(screen.getByRole('button', { name: 'Favorit' })).toBeInTheDocument();
+	});
+
+	it('has correct aria-label when active', () => {
+		render(FavoriteButton, {
+			props: { active: true, onclick: vi.fn() },
+		});
+		expect(screen.getByRole('button', { name: 'Favorit entfernen' })).toBeInTheDocument();
+	});
+
+	it('calls onclick when clicked', async () => {
+		const onclick = vi.fn();
+		render(FavoriteButton, { props: { active: false, onclick } });
+		await fireEvent.click(screen.getByRole('button'));
+		expect(onclick).toHaveBeenCalledOnce();
+	});
+
+	it('uses pin labels for pin variant', () => {
+		render(FavoriteButton, {
+			props: { active: false, onclick: vi.fn(), variant: 'pin' },
+		});
+		expect(screen.getByRole('button', { name: 'Anpinnen' })).toBeInTheDocument();
+	});
+
+	it('uses custom label when provided', () => {
+		render(FavoriteButton, {
+			props: { active: false, onclick: vi.fn(), label: 'Custom' },
+		});
+		expect(screen.getByRole('button', { name: 'Custom' })).toBeInTheDocument();
+	});
+});