Fix Delete key behaviour and improve element validation

[rounittxx]

This PR Fixes the Delete key shortcut not triggering the deletion logic in the editor.

Summary of changes:

• Added useEffect to handle Delete/Backspace key events at the component level
• Corrected layout.readonly → layout.readOnly
• Added a validation check to ensure a valid selectedElement before calling the delete function

Using useEffect ensures that Delete and Backspace work consistently across tables, notes, areas matching the behaviour documented in the shortcuts list.

Tested on macOS + Chrome (normal & incognito).

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[rounittxx]

@1ilit kindly review my pr and let me know if any changes are needed :)

[rounittxx]

i found a better way to solve the issue