Add a fullscreen button (or menu option) for in-car browsers

Many EVs ship with a built-in web browser that runs alongside the native navigation in split view — which makes the ABRP web app a perfect companion: native nav on one side, ABRP with live charger availability on the other, no Android Auto or CarPlay needed (which would replace the car's own navigation entirely).

The problem: these car browsers permanently show their address bar and offer no way to enter fullscreen. Example XPeng (G6, Xmart OS): the browser is a desktop Chromium 120, but the menu has no fullscreen entry, F11 is not available, bookmarklets and javascript: URLs are blocked, and there is no "install app" option. So the address bar permanently eats screen height that the map could use — and there is nothing the user can do about it from outside the page.

The fix only ABRP can provide, and it's small: a fullscreen toggle inside ABRP itself. A tap on it is a genuine user gesture on ABRP's own page, which is exactly what the Fullscreen API requires. Since ABRP is a single-page app, fullscreen survives all in-app navigation. Other map sites already do this — e.g. Windy has a fullscreen button and works perfectly in the same car browser. Mapbox GL even ships a ready-made FullscreenControl for this.

Alternatively (or additionally): restoring the web app manifest with display: "fullscreen" would let capable browsers install ABRP without any UI chrome. ABRP had an installable PWA manifest until early 2024; the Expo migration removed it.

Either option would unlock the full ABRP experience in a growing number of cars whose browsers coexist with the native nav — exactly the situation where ABRP + live data shines.