### 1. Replace `XMLHttpRequest` with the modern `fetch` API for loading
translation files
#### Changes
- **translator.js**: Use `fetch` with `async/await` instead of XHR
callbacks
- **loader.js**: Align URL handling and add error handling (follow-up to
fetch migration)
- **Tests**: Update infrastructure for `fetch` compatibility
#### Benefits
- Modern standard API
- Cleaner, more readable code
- Better error handling and fallback mechanisms
### 2. Migrate e2e tests to Playwright
This wasn't originally planned for this PR, but is related. While
investigating suspicious log entries which surfaced after the fetch
migration I kept running into JSDOM’s limitations. That pushed me to
migrate the E2E suite to Playwright instead.
#### Changes
- switch e2e harness to Playwright (`tests/e2e/helpers/global-setup.js`)
- rewrite specs to use Playwright locators + shared `expectTextContent`
- install Chromium via `npx playwright install --with-deps` in CI
#### Benefits
- much closer to real browser behaviour
- and no more fighting JSDOM’s quirks
read index.html to discover the regions used, make them the list checked
by app.js and check:config test
fixes#3504 supercedes #3506
no config.js param required
