Register touch event handlers (touchstart, touchmove, touchend) that call existing mouse handlers and prevent default scrolling (passive: false) so the canvas can be interacted with on touch devices. Update getGridPosition to accept TouchEvent or MouseEvent, read touch coordinates, and apply canvas-to-CSS scaling (canvas.width/rect.width and canvas.height/rect.height) to correctly map client coordinates to grid cells. This enables accurate touch interaction and handles high-DPI / CSS-scaled canvases.
