Memory game: grid overflows viewport on narrow mobile screens

[KovalDenys1]

On mobile, the memory grid can exceed the viewport width. Needs same viewport-relative constraint as TTT/C4 board size fix.

[KovalDenys1]

Already fixed. .memory-grid uses width: min(100%, 780px) (desktop) and .memory-mobile-board-wrap uses width: min(calc(100vw - 24px), ...) (mobile) — grid cannot overflow viewport.