Implement RespawnAreaDoor and refactor physics collision layers
- Add RespawnAreaDoor class for interactable doors.
- Rename physics layers: Static to Solid and Moving to Ephemeral.
- Remove Visibility physics layer and simplify collision filtering.
- Update loot, particles, and meshes to use new collision layers.
- Add door icon and respawn area door assets.
Finally, I’m back to working on game content and not just systems. Even while working on the door, I still had to touch some low-level systems, but I polished up the collision layering. I think the current setup makes more sense.