Improve Enemy Interaction With Environment (Ghosts Ignore Obstacles)

## Description
Ghost enemies currently pass through most obstacles. While this initially feels interesting, it ends up reducing meaningful player movement and removes the ability to use cover or positioning strategically. As a result, many obstacles feel irrelevant from a gameplay perspective.

## Expected Improvement
- Introduce at least some enemies or situations where obstacles matter
- Allow players to use environment features for positioning, avoidance, or crowd control
- Improve "crowd management" so the player must move and make spatial decisions

## Notes
- Ghosts could selectively pass through certain objects
- Mix enemy types: some that respect collision, some that don’t
- Consider temporary barriers or elemental interactions that affect ghosts