Feature - Support background Reference/Tracing Image

[DevGeniusCode]

Title:
Feature: Support background Reference/Tracing Image on the canvas

Description:
To help modders recreate original game menus accurately, they need the ability to load a static blueprint image (mockup or screenshot) into the background of the canvas to trace over.

Tasks:

• Add a menu option / toolbar button to "Load Reference Image" (supporting PNG/JPG for now).
• Render this image on the QGraphicsScene at the absolute lowest Z-Index (always behind all UI controls).
• Lock the image so it cannot be selected or accidentally moved by the user (ItemIsSelectable = False).
• Ensure the parsing/saving logic completely ignores this background item so it doesn't get exported into the .wnd file.

Acceptance Criteria:

• Image loads and scales correctly on the canvas.
• UI elements can be drawn directly on top of the image.
• Clicking on the canvas does not select the reference image.
• Saving the project does not include the reference image in the exported output.