[v0.0.6] Fix Inventory Item Management

[jacuzzicoding]

Description

Fix issues with inventory item management, specifically related to item stacking, movement between slots, and quantity tracking. Currently, inventory management is buggy with inconsistent stacking behavior and issues when breaking rocks or other resources.

Requirements

• Fix item stacking logic to ensure consistent behavior
• Implement proper item quantity tracking
• Fix issues with resources taking multiple inventory slots
• Improve drag-and-drop reliability
• Add support for splitting and combining item stacks

Technical Details

Current issues:

• Breaking rocks causes items to take two inventory slots with quantities changing randomly
• Item movement in inventory is extremely buggy
• Inconsistent stacking behavior
• No ability to split or combine stacks

Acceptance Criteria

• Items stack properly when collected
• Items can be moved reliably between inventory slots
• Resources consistently take single slots with proper quantities
• Players can split stacks (e.g., by shift-clicking)
• Players can combine stacks of the same item type
• Hotbar selection works consistently with inventory