feat: 更新截图功能，修复截图框样式

Author: qdaxb

src/pages/Screenshot/components/Editor/SelectionBorder.tsx

@@ -9,14 +9,25 @@ interface SelectionBorderProps {
   canvasOffsetX: number;
   pinned: boolean;
   onHandleMouseDown: (e: React.MouseEvent, key: HandleType) => void;
+  /**
+   * 移动模式下边框的屏幕绝对位置（fixed 定位基准）。
+   * 非移动模式下为 null，此时使用相对于 Editor 容器的 absolute 定位。
+   */
+  fixedOrigin?: { x: number; y: number } | null;
 }
 
 const SelectionBorder: React.FC<SelectionBorderProps> = ({
   currentSel,
   canvasOffsetX,
   pinned,
   onHandleMouseDown,
+  fixedOrigin,
 }) => {
+  // 移动模式：用 fixed + 屏幕绝对坐标；否则用 absolute + 相对容器坐标
+  const useFixed = Boolean(fixedOrigin);
+  const originX = fixedOrigin ? fixedOrigin.x : 0;
+  const originY = fixedOrigin ? fixedOrigin.y : 0;
+
   const handles: { key: HandleType; x: number; y: number }[] = [
     { key: "nw", x: canvasOffsetX + 0, y: 0 },
     { key: "n", x: canvasOffsetX + currentSel.w / 2, y: 0 },
@@ -38,10 +49,10 @@ const SelectionBorder: React.FC<SelectionBorderProps> = ({
             "0 0 0 1.5px rgba(0,0,0,0.5), 0 4px 24px rgba(0,0,0,0.6), inset 0 0 12px rgba(0,0,0,0.25)",
           boxSizing: "border-box",
           height: currentSel.h,
-          left: canvasOffsetX,
+          left: useFixed ? originX + canvasOffsetX : canvasOffsetX,
           pointerEvents: "none",
-          position: "absolute",
-          top: 0,
+          position: useFixed ? "fixed" : "absolute",
+          top: useFixed ? originY : 0,
           width: currentSel.w,
           zIndex: 21,
         }}
@@ -61,9 +72,13 @@ const SelectionBorder: React.FC<SelectionBorderProps> = ({
               boxSizing: "border-box",
               cursor: getHandleCursor(key),
               height: HANDLE_SIZE + 4,
-              left: x - (HANDLE_SIZE + 4) / 2,
-              position: "absolute",
-              top: y - (HANDLE_SIZE + 4) / 2,
+              left: useFixed
+                ? originX + x - (HANDLE_SIZE + 4) / 2
+                : x - (HANDLE_SIZE + 4) / 2,
+              position: useFixed ? "fixed" : "absolute",
+              top: useFixed
+                ? originY + y - (HANDLE_SIZE + 4) / 2
+                : y - (HANDLE_SIZE + 4) / 2,
               width: HANDLE_SIZE + 4,
               zIndex: 22,
             }}