enqueue casts when other skills are animating;

made curvature more smooth in short drags;
adjusted line head pivot so it's pointing to actual mouse position;

major code rewrite;
fixed some dragging logic;
added a discard indicator next to Discard Button when dragging;
made some behaviours more intuitive;

added GamePlay tag;

added amazing asset from 七叶咕咕!
added arrow head at the end of line;
hides cursor when dragging;

fixed various drag release logic;
added cancel button;

允许同时使用原版和拖拽换牌方式

Fixed various UI logic bugs;
Optimized enemy UI detection so it doesn't block dragging;
Fixed skills are still draggable while being disabled;
Fixed a few hovering logic;

remove game asset