Bug: Game State Not Reset When Returning to Menu

## Description
On the first run, returning to the menu and restarting the game causes the second level to stop spawning enemies.

## Steps to Reproduce
- Start a new game
- Return to the menu
- Restart the game
- Progress to the second level

## Expected Behavior
- Enemy spawning should function correctly after restarting

## Actual Behavior
- Second level does not spawn enemies

## Suspected Cause
- Game data or state is not properly reset when returning to the menu

## Notes
- Likely related to singleton data, static variables, or wave manager state
- High priority bug as it blocks progression