Fixed three issues that caused tunneling:

1. **Sub-stepping**: Movement + collision is now split into 4 sub-steps per frame (both intro and main game), so the player moves in smaller increments and can't skip through objects in a single frame.

2. **Iterative collision resolution**: `checkShapeCollisions` now loops up to 3 times per sub-step — if the player is still overlapping any shape after being pushed out, it resolves again. This handles edge cases where bouncing off one shape pushes into another.

3. **Velocity-aware bouncing**: Velocity is only reversed if the player is actually moving *into* the shape, preventing double-bounces that could shoot the player through. Small epsilon values on push-out ensure clean separation.

**Next Ideas:**
1. **Visual bounce feedback** - Add a brief squash/stretch animation or screen shake when the person collides with objects
2. **Collision particles** - Spawn small sketchy particle bursts on impact to make bounces feel more satisfying

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