- Create ReactionPicker component with 24 common emoji options
- Show emoji grid in dialog with proper styling
- Update PostActions to show picker instead of default heart
- Add _showReactionPicker method with showDialog
- Update ReactionStrip onAdd callback to use picker
- Maintain full reaction functionality with user choice
- Add proper styling with borders and shadows to picker
- Replace NULLIF with CASE WHEN for proper UUID casting
- Fix missing ::uuid casting in WHERE clauses
- Resolve 'operator does not exist: uuid = text' errors
- Focus on post_repository.go, notification_repository.go, and category_repository.go