After selecting the build control mode, the build map grid will be displayed, green means you can build, red means you can't, and you can only build in the area where the map grid is displayed.
Before: Build position is based on the mouse position.
Now: Only the center of the grid can be built, and only one building can be built in a grid area.
Other notes:
This addition is in preparation for adding more buildings and adding a pathfinding system for characters in the future.
Fixed the problem that the maximum number of buildings would not be initialized when restarting the game.