Non-quadratic tiles in Tiny chess mode by default

Description:
When opening Tiny chess the window has the same default size as it normally has, which skews the tiles. Not sure whether this deserves a fix, as no other game mode probably needs to change the default window size.

No file or test is named. Start by locating the Tiny chess mode initialization and the code that sets the default window size or tile dimensions; confirm the issue by opening Tiny chess and checking whether the tiles are non-square. Done means Tiny chess opens with square tiles without changing the default sizing behavior of other game modes.

Written by the indexing model from the issue text.