Done! I've updated the collision system:

**Changes made:**
- Increased zombie stopping distance from 1.0 to 2.5 units around player
- Increased zombie-to-zombie collision distance from 1.2 to 1.5 units
- Increased attack range from 2.5 to 3.0 units to match the new collision radius

Zombies now maintain a visible radius around you, preventing them from stacking directly on top of the player so you can see and shoot them.

**Next Ideas:**
1. **Add Melee Attack** - Press F to knife zombies in close range when ammo runs low
2. **Zombie Variants** - Create fast runners, tank zombies, or exploders with unique behaviors and colors

**Ready to level up your game? Pick one and let's build it!**