Links outside Lichess should not be opened in-app

## Description
As this app is basically a chopped down browser, opening links not related to Lichess is still possible. While this doesn't sound so bad, it actually breaks the functionality, as all browser navigation possibilities are not present.

**Solution:** The app should redirect any outside links to another browser or app on the phone

## To Reproduce
1. go on the Lichess start page
2. click on any outside link ("swag store", twitch,...)

Start at the Lichess start page and reproduce the problem by opening an outside link such as the swag store or Twitch. Trace the app's link-handling or navigation entry point, then verify that outside links open in another browser or phone app while Lichess links remain in-app.

Written by the indexing model from the issue text.