feat(V0.2): 拖动跟手浮层 —— 半透明副本随指针, 原位虚线占位

- useRowDrag/useHabitDrag 暴露 ghostRef, 拖动激活与移动时直接改
  transform (绕过 React 重渲染, 保证跟手流畅)
- 打卡浮层带颜色点 + 名称; 任务列表浮层带任务名 + 实时目标列名
- 原位卡片降为低透明度虚线占位, 落点指示不变

src/components/task/useRowDrag.js

@@ -33,6 +33,12 @@ export default function useRowDrag({ columns, onDrop }) {
   /** 拖动刚结束 (350ms 内): 抑制松手合成的 click 误开详情页 */
   const justEnded = useCallback(() => Date.now() - lastEnd.current < 350, [])
 
+  // 跟手浮层: 消费方渲染 <div ref={ghostRef}>, 拖动时直接改 transform
+  const ghostRef = useRef(null)
+  const moveGhost = (x, y) => {
+    if (ghostRef.current) ghostRef.current.style.transform = `translate(${x}px, ${y}px) translate(-50%, -110%)`
+  }
+
   const onMove = (ev) => {
     const s = st.current
     if (!s.active) {
@@ -42,6 +48,7 @@ export default function useRowDrag({ columns, onDrop }) {
       return
     }
     ev.preventDefault()
+    moveGhost(ev.clientX, ev.clientY)
     const to = Math.max(0, Math.min(ordered.length - 1, s.fromIdx + Math.round((ev.clientX - s.startX) / STEP)))
     if (to !== s.toIdx) {
       s.toIdx = to
@@ -99,6 +106,7 @@ export default function useRowDrag({ columns, onDrop }) {
         st.current.active = true
         if (navigator.vibrate) navigator.vibrate(15)
         setDrag({ task, fromIdx, toIdx: fromIdx })
+        moveGhost(st.current.startX, st.current.startY)
       }, 400)
       armListeners(ev)
     },
@@ -120,11 +128,12 @@ export default function useRowDrag({ columns, onDrop }) {
       st.current.active = true
       if (navigator.vibrate) navigator.vibrate(15)
       setDrag({ task, fromIdx, toIdx: fromIdx })
+      moveGhost(st.current.startX, st.current.startY)
       armListeners(ev, true)
     },
     onContextMenu: (ev) => ev.preventDefault(),
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }), [ordered, onDrop])
 
-  return { drag, bind, bindHandle, cancel: cleanup, justEnded }
+  return { drag, bind, bindHandle, ghostRef, cancel: cleanup, justEnded }
 }