On iOS (notably the Telegram Mini App) the document elastic-overscrolls on a
vertical drag even with overscroll-behavior:none — the whole page stretches and
bounces, and it fought the board's swipe-to-open-history. Telegram's own
swipe-to-minimise is already disabled at launch; this removes the remaining
WebKit document bounce by pinning the document (position:fixed + overflow:hidden)
for the game SPA only. Every screen already fits the visual viewport (--vvh) and
scrolls its own inner areas, so the document never needed to scroll.
Scoped to the app via an `app-shell` class set in main.ts; the standalone
landing page (landing.ts) keeps its normal scrolling document. e2e locks the
contract on both entries.
Ilia Denisov