Problem: dispatchEvent('input') doesn't trigger React's onChange in React 17+.
Solution: pass onCategoryEnter callback from ChatInputArea to MentionPopover.
When Enter is pressed on a category, MentionPopover calls onCategoryEnter(category)
which directly calls React setState (onDraftChange, setCursorPosition,
setShowMentionPopover) inside ChatInputArea, properly triggering re-render.