- Implemented dual overlay system with command-line switchable options (--overlay-type webengine/native)
- Fixed critical Qt player window close to properly exit entire application
- Restored and enhanced Ctrl+C signal handling functionality
- Added admin-only quit button to web dashboard with guaranteed force termination
- Fixed background thread management with proper daemon threads
- Resolved WebEngine JavaScript timing errors with enhanced DOM readiness checks
- Eliminated desktop transparency bleed-through issues
- Removed video controls for clean overlay-only interface
- Prevented circular dependency deadlocks in shutdown process
- Enhanced Qt threading architecture and signal integration
- Updated comprehensive documentation and changelog

Technical fixes:
- closeEvent() in Qt player now allows proper Qt shutdown sequence
- signal_handler() enhanced to detect Qt applications and use qt_app.quit()
- ThreadManager modified to set daemon=True for all background threads
- Added /api/system/shutdown endpoint with force-exit mechanism using os._exit(0)
- Enhanced aboutToQuit signal handling for proper lifecycle management
- WebEngine overlay safety improved with comprehensive error handling