perf: parallelize file uploads and add consistent drag validation

Use Promise.all for concurrent file uploads instead of sequential
processing, improving upload performance for multiple files. Also
add isFileDrag check to handleFolderDragOver for consistency with
other drag handlers.

web/app/components/workflow/skill/hooks/use-file-drop.ts

@@ -71,14 +71,16 @@ export function useFileDrop() {
       return
 
     try {
-      for (const file of files) {
-        await createFile.mutateAsync({
-          appId,
-          name: file.name,
-          file,
-          parentId: targetFolderId,
-        })
-      }
+      await Promise.all(
+        files.map(file =>
+          createFile.mutateAsync({
+            appId,
+            name: file.name,
+            file,
+            parentId: targetFolderId,
+          }),
+        ),
+      )
 
       Toast.notify({
         type: 'success',

web/app/components/workflow/skill/hooks/use-folder-file-drop.ts

@@ -62,7 +62,7 @@ export function useFolderFileDrop(node: NodeApi<TreeNodeData>): UseFolderFileDro
   }, [isFolder, scheduleAutoExpand])
 
   const handleFolderDragOver = useCallback((e: React.DragEvent) => {
-    if (!isFolder)
+    if (!isFolder || !isFileDrag(e))
       return
     handleDragOver(e, { folderId: node.data.id, isFolder: true })
   }, [handleDragOver, isFolder, node.data.id])