WIP: Add E2E UI smoke test to run in BrowserStack

[rwood-moz]

What changed?

Add a separate set of E2E tests that can run against stormbox stage or prod in BrowserStack.

Why?

The existing E2E tests in /tests/e2e (which run in CI against PRs) require a local stormbox dev stack which they make direct DB/cache/JMAP calls etc. and are not built to run in BrowserStack against a deployed stormbox instance; so adding a separate set of E2E tests specifically to be able to run in BrowserStack.

Details

Added a standalone BrowserStack E2E test package under tests/browserstack for UI-only testing against deployed Stormbox stage/prod. This includes its own package.json, package-lock.json, tsconfig.json, and pinned dependencies for Playwright 1.59.1, BrowserStack SDK 1.57.2, and dotenv 16.6.1.

Implemented desktop and mobile ui-smoke coverage that signs in through the Stormbox UI using TB Pro credentials from .env.browserstack, then verifies the basic authenticated Stormbox UI appears. Desktop uses a dedicated tests/desktop/auth.desktop.ts setup file to save auth state, while mobile signs in per test.

Added shared constants, auth helpers, and a Stormbox page object for the new suite. Updated the BrowserStack Playwright config to load .env.browserstack and match auth.desktop.ts.

Added tests/browserstack/README.md documenting that these tests target deployed stage/prod only, not the local stack, with setup and run instructions for local Playwright and BrowserStack runs. Added tests/browserstack/.env.browserstack to .gitignore so credentials stay local.

Limitations and Notes

This patch will add a UI smoke test that will run in BrowserStack on Firefox, Chromium, and Safari desktop, as well as on Chrome on a real Google Pixel 10 device. More tests will be added to this suite in future PRs.

Worked with Codex AI to get the initial framework and test in place, then further refined the code and the test myself.

Applicable Issues

Fixes #17.

QA Log

Ran this new set of E2E tests:

• Firefox desktop on my local machine
• Playwright's simulated google pixel 10 viewport on my local machine
• Firefox desktop on OSX on BrowserStack [todo]
• Chromium desktop on Win 11 on BrowserStack [todo]
• Safari desktop on OSX on BrowserStack [todo]
• Android chrome on a Google Pixel 10 device on BrowserStack [todo] * note: test skips as expected because BrowserStack doesn't support Android Chrome 148+ yet and that is needed for Stormbox (sharedworkers) *
• iOS Safari on an iPhone 17 device on BrowserStack [todo]
• iOS Safari on an iPad 13 device on BrowserStack [todo]