Add storage containers

[dmccoystephenson]

Summary

Add craftable storage containers that can be placed in the world, accessed by right-clicking, and persisted between sessions.

Background

Currently the only way to store items outside the player's inventory is to place them directly in the world, which is lossy and inconvenient. A dedicated storage container entity would give players a proper item management option.

Requirements

Entity

• Add a Chest entity (src/entity/chest.py) — solid, placeable, with a placeholder asset (assets/images/chest.png)

Crafting

• Add a Chest recipe to RecipeRegistry (src/crafting/recipeRegistry.py), e.g. 6× OakWood

Interaction

• Right-clicking a placed Chest in the world opens a chest inventory screen (similar to InventoryScreen)
• The chest screen should display the chest's contents and allow items to be moved in/out
• Left-click outside the chest panel drops cursor items (consistent with InventoryScreen behaviour)

Persistence

• Chest contents must survive save/load cycles
• Extend RoomJsonReaderWriter (src/world/roomJsonReaderWriter.py) to serialize/deserialize Chest entities and their contents
• Follow the existing entity registry pattern in inventoryJsonReaderWriter.py and roomJsonReaderWriter.py when adding the new entity type

Pickup

• Add Chest to the canBePickedUp() check in worldScreen.py (only when empty, to prevent item loss)

Acceptance Criteria

• Chest can be crafted and placed in the world
• Right-clicking a chest opens its inventory UI
• Items can be moved between the player's inventory and the chest
• Chest contents are saved to the room JSON and restored on load
• A non-empty chest cannot be picked up
• All existing tests pass; new tests cover chest save/load and the canBePickedUp guard