True Backpack (+ Quiver & Helipack)

Small update on backpacks and equipment:

• Added a simple 3-slot backpack crafted using fibre.
• The Helipack now only handles fuel internally, making its role more focused.
• Backpacks now interact with death mechanics: if your world is set to drop items on death, any backpack in your inventory will drop as well. Instead of spilling its contents, it acts like a grave, safely holding everything until you retrieve it.

Let me know your thoughts!