testing-e2e-with-playwright

@sumik5

Playwright E2Eテストの設計・実装・運用ガイド。 Use when writing, reviewing, or maintaining E2E tests with @playwright/test. playwright.config.* 検出時に自動ロード。testing-code（テスト全般）とは異なりPlaywright E2E固有のパターンに特化。