fix: 恢复画布 overflow-hidden 防止内容溢出覆盖工具栏

工具栏已使用 Portal 渲染，不再需要 overflow-visible

Co-authored-by: Cursor <cursoragent@cursor.com>

components/canvas/CanvasWorkspace.tsx

@@ -217,7 +217,7 @@ export function CanvasWorkspace() {
     <div
       ref={containerRef}
       className={cn(
-        "relative w-full h-full overflow-visible bg-background",
+        "relative w-full h-full overflow-hidden bg-background",
         tool === 'pan' && "cursor-grab",
         isPanning && "cursor-grabbing"
       )}