Update README with sync features and device cap

- Document universal sync system
- Add device cap management feature
- Note SSL/TLS proxy configuration
- Include API endpoints and features overview

README.md

@@ -40,6 +40,17 @@ A modern self-hosted media library system built with Go, PostgreSQL, HTMX, and T
 - **Mobile-First Design**: Fully responsive interface for all devices
 - **HTMX Integration**: Dynamic interactions without page reloads
 
+### 🔄 Universal Cross-Platform Sync (NEW!)
+- **Real-Time Progress Sync**: Reading progress syncs automatically across all your devices
+- **Multi-Device Support**: KOReader, Kobo e-readers, web browsers, mobile apps
+- **Format-Aware Tracking**: EPUB CFI, page numbers, percentages, character offsets
+- **Highlights & Notes**: Annotations sync universally across all devices
+- **Conflict Resolution**: Smart handling when same book read on multiple devices
+- **Offline Support**: Queue changes when offline, sync when reconnected
+- **Secure Device Auth**: Web-based device approval, no passwords on devices
+- **Checkpoint Mode**: Batch sync for better battery life
+- **WebSocket Updates**: Real-time broadcast of progress changes
+
  ### 📱 Media Management
  - **Universal Media Support**: Single system for all media types with unified interface
  - **Rich Metadata**: Automatic extraction of title, author, series, publisher, ISBN, tags