Add comprehensive messenger features and improvements
- Backend improvements: flexible user authentication, nullable fields
- Frontend enhancements: new screens (NewMessage, UserInfo), improved UI/UX
- Chat functionality: real-time messaging with polling, message actions
- Visual upgrades: gradient backgrounds, better themes, modern design
- Added project documentation (CLAUDE.md) and development guidelines
🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>
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