Prevent crash when dragging a folder into its own child

[Gopmyc]

Description

This PR fixes a crash in the Asset Browser when a folder is dragged and dropped into one of its own descendants.

The fix adds a local guard in the folder drag-and-drop handler to detect invalid parent->child (or self) moves before filesystem rename/copy operations are executed.
When such a move is detected, the operation is safely ignored and a warning is logged.

Related Issue(s)

Fixes #699

Review Guidance

Please focus review on:

• Folder DDTarget logic in AssetBrowser.cpp
• The new path ancestry guard used before move/copy operations
• Regression risk on valid drag/drop scenarios (project/project and engine/project)

Screenshots/GIFs

N/A (behavioral crash fix; no UI change)

Checklist

• My code follows the project's code style guidelines
• I have commented my code, particularly in hard-to-understand areas
• I have updated the documentation accordingly
• My changes don't generate new warnings or errors