contenteditable="true" from column divs to prevent nested contenteditable elements.
Root Cause: Column divs had contenteditable="true" while being nested inside the main editor (also contenteditable="true").
Impact: Nested contenteditable elements cause paste events to fire multiple times, leading to duplicate content insertion.
Fix: Removed contenteditable="true" attribute from column divs in ColumnPlugin.js.
Benefit: Columns remain editable through inheritance from the parent editor, but paste events only fire once.
src/plugins/ColumnPlugin.js - Removed contenteditable from lines 182, 235__tests__/ColumnPlugin.test.js - Updated tests to verify no contenteditable on columns__tests__/ColumnPasteBehavior.test.js - Added new tests for paste behavior