Added a proper level selector dialog using MUI’s Dialog and Chip components. When you complete a level, the selector automatically pops up so you can pick the next challenge. Completed levels show with a filled chip style while unselected ones remain outlined.

Fixed a few bugs along the way: player spawn positions weren’t calculating correctly, wall goals had rendering issues, and users could accidentally delete goal cells in the level editor. Now goal cells are protected from deletion to prevent breaking levels mid-edit.