Save/Load Drawing JSON

[pexeixv]

Goal:
Allow users to save their current drawing and load it later.

Requirements:

• Buttons: "Save JSON" and "Load JSON".
• JSON should store all cell colors and optionally history.
• Loading restores the grid and integrates with Undo/Redo.

Notes:
Enables users to keep their work for later editing.

[MonarchRyuzaki]

Hi @pexeixv @ctrl-7 , I would like to work on this. Can you assign it to me?