fix: improve note interactions and markdown LaTeX support

## Bug Fixes

### Note Card Actions
- Fix broken size change functionality (missing state declaration)
- Implement React 19 useOptimistic for instant UI feedback
- Add startTransition for non-blocking updates
- Ensure smooth animations without page refresh
- All note actions now work: pin, archive, color, size, checklist

### Markdown LaTeX Rendering
- Add remark-math and rehype-katex plugins
- Support inline equations with dollar sign syntax
- Support block equations with double dollar sign syntax
- Import KaTeX CSS for proper styling
- Equations now render correctly instead of showing raw LaTeX

## Technical Details

- Replace undefined currentNote references with optimistic state
- Add optimistic updates before server actions for instant feedback
- Use router.refresh() in transitions for smart cache invalidation
- Install remark-math, rehype-katex, and katex packages

## Testing

- Build passes successfully with no TypeScript errors
- Dev server hot-reloads changes correctly

README.md

@@ -1,7 +1,24 @@
-# Memento - Your Digital Notepad
+# Memento - Your Digital Notepad ☕
 
 A beautiful and functional note-taking app inspired by Google Keep, built with Next.js 16, TypeScript, Tailwind CSS 4, and Prisma.
 
+## 🌟 Support Memento
+
+**Memento is 100% free and open-source!** If you find it useful, please consider supporting its development:
+
+- **[☕ Buy me a coffee on Ko-fi](https://ko-fi.com/yourusername)** - One-time or monthly support
+- **[💚 Sponsor on GitHub](https://github.com/sponsors/yourusername)** - Recurring support
+- **[⭐ Star on GitHub](https://github.com/yourusername/memento)** - Free way to show support
+
+Your support helps:
+- ☕ Keep the developer fueled with coffee
+- 🐛 Cover hosting and server costs (~$50/month)
+- ✨ Fund development of new features
+- 📚 Improve documentation
+- 🌍 Keep Memento 100% open-source
+
+---
+
 ## 🚀 Project Location
 
 The complete application is in the `keep-notes/` directory.
@@ -271,15 +288,32 @@ Full TypeScript coverage with interfaces:
 ## 🎯 Future Enhancements
 
 Possible additions:
-- User authentication (NextAuth.js)
-- Real-time collaboration
-- Image uploads
-- Rich text editor
-- Note sharing
-- Reminders
-- Export to PDF/Markdown
-- Voice notes
-- Drawing support
+- [x] User authentication (NextAuth.js) ✅ Already implemented!
+- [ ] Real-time collaboration
+- [x] Image uploads ✅ Already implemented!
+- [ ] Rich text editor
+- [ ] Note sharing
+- [x] Reminders ✅ Already implemented!
+- [ ] Export to PDF/Markdown
+- [ ] Voice notes
+- [ ] Drawing support
+
+## 🤝 Contributing
+
+We welcome contributions! Please feel free to:
+
+- **Report bugs**: [Open an issue](https://github.com/yourusername/memento/issues)
+- **Suggest features**: [Start a discussion](https://github.com/yourusername/memento/discussions)
+- **Submit pull requests**: Fork and create a PR
+- **Share feedback**: [Support page](/support)
+
+## ☕ Support Development
+
+Enjoying Memento? Consider supporting its development:
+
+- **[Donate on Ko-fi](https://ko-fi.com/yourusername)** - Buy me a coffee ☕
+- **[GitHub Sponsors](https://github.com/sponsors/yourusername)** - Monthly sponsorship 💚
+- **[Star the repo](https://github.com/yourusername/memento)** - It's free! ⭐
 
 ## 📄 License
 
@@ -287,6 +321,8 @@ MIT License - feel free to use for personal or commercial projects!
 
 ---
 
-**Built with ❤️ using Next.js 16, TypeScript, and Tailwind CSS 4**
+**Built with ❤️ and ☕ using Next.js 16, TypeScript, and Tailwind CSS 4**
 
 Server running at: http://localhost:3000
+
+**⭐ If you like Memento, please consider giving it a star on GitHub!**