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-stores/src/toggle-field.test.ts

@@ -0,0 +1,49 @@
+import { describe, it, expect, vi } from 'vitest';
+import { toggleField } from './toggle-field';
+
+function createMockTable(records: Record<string, Record<string, unknown>>) {
+	return {
+		get: vi.fn(async (id: string) => records[id] ?? null),
+		update: vi.fn(async (id: string, changes: Record<string, unknown>) => {
+			if (records[id]) Object.assign(records[id], changes);
+			return 1;
+		}),
+	};
+}
+
+describe('toggleField', () => {
+	it('toggles false to true', async () => {
+		const table = createMockTable({ '1': { id: '1', isFavorite: false } });
+		const result = await toggleField(table as never, '1', 'isFavorite');
+		expect(result).toBe(true);
+		expect(table.update).toHaveBeenCalledWith('1', expect.objectContaining({ isFavorite: true }));
+	});
+
+	it('toggles true to false', async () => {
+		const table = createMockTable({ '1': { id: '1', isFavorite: true } });
+		const result = await toggleField(table as never, '1', 'isFavorite');
+		expect(result).toBe(false);
+		expect(table.update).toHaveBeenCalledWith('1', expect.objectContaining({ isFavorite: false }));
+	});
+
+	it('sets updatedAt timestamp', async () => {
+		const table = createMockTable({ '1': { id: '1', isPinned: false } });
+		await toggleField(table as never, '1', 'isPinned');
+		const call = table.update.mock.calls[0][1] as Record<string, unknown>;
+		expect(call.updatedAt).toBeTruthy();
+		expect(typeof call.updatedAt).toBe('string');
+	});
+
+	it('throws if record not found', async () => {
+		const table = createMockTable({});
+		await expect(toggleField(table as never, 'missing', 'isFavorite')).rejects.toThrow(
+			'Record missing not found'
+		);
+	});
+
+	it('treats undefined as false', async () => {
+		const table = createMockTable({ '1': { id: '1' } });
+		const result = await toggleField(table as never, '1', 'isFavorite');
+		expect(result).toBe(true);
+	});
+});