Move mail, compose, contacts, and accounts off mocks onto REST + WS.
Add client, auth store, IDB-backed query cache, offline queue, and
sync bar; hybrid Zustand for UI-only state. Settings still local until
backend has preferences API.
- Added Playwright as a dependency for end-to-end testing, including necessary scripts in package.json.
- Created a Playwright configuration file to define test settings and browser options.
- Implemented a new GitHub Actions workflow for automated end-to-end testing on push and pull request events.
- Updated .gitignore to exclude Playwright test results and reports.
- Added initial end-to-end tests for mail functionalities, including composing, sending, and searching messages.
