e30f02f9fe
- Add DragDropHandler class with unified mouse + touch events - Implement ghost element preview during drag - Add grid overlay with cell highlighting - Support touch events with 150ms delay for scroll compatibility - Add Escape key to cancel drag - Complete lifecycle management (init, destroy, cleanup) - Create mobile-ready test harness with: - Touch-optimized UI (44px touch targets) - Responsive grid layout - Real-time event logging - Add/remove/reflow widgets - Works on desktop and mobile - 420 lines core code, 880 lines test suite - Comprehensive JSDoc documentation