Optimizations, bug/crash fixes, a new boss, and better heat management

What has changed:

• Optimized performance through code refactoring.
• Fixed UI bugs for a smoother experience.
• Resolved a crash tied to the background animation.
• Added a placeholder boss at depth 100 (defeating it doesn’t end the game yet).
• Adjusted coal heat output to reduce frustrating temperature overshooting.

More updates coming soon!