Add support for dragging in multiple workflow files at once (#8757)

## Summary

Allows users to drag in multiple files that are/have embedded workflows
and loads each of them as tabs.
Previously it would only load the first one.

## Changes

- **What**: 
- process all files from drop event
- add defered errors so you don't get errors for non-visible workflows

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8757-Add-support-for-dragging-in-multiple-workflow-files-at-once-3026d73d365081c096e9dfb18ba01253)
by [Unito](https://www.unito.io)

src/scripts/app.test.ts

@@ -85,11 +85,7 @@ describe('ComfyApp', () => {
 
       const file1 = createTestFile('test1.png', 'image/png')
       const file2 = createTestFile('test2.jpg', 'image/jpeg')
-      const dataTransfer = new DataTransfer()
-      dataTransfer.items.add(file1)
-      dataTransfer.items.add(file2)
-
-      const { files } = dataTransfer
+      const files = [file1, file2]
 
       await app.handleFileList(files)
 
@@ -110,26 +106,21 @@ describe('ComfyApp', () => {
       vi.mocked(createNode).mockResolvedValue(null)
 
       const file = createTestFile('test.png', 'image/png')
-      const dataTransfer = new DataTransfer()
-      dataTransfer.items.add(file)
 
-      await app.handleFileList(dataTransfer.files)
+      await app.handleFileList([file])
 
       expect(mockCanvas.selectItems).not.toHaveBeenCalled()
       expect(mockNode1.connect).not.toHaveBeenCalled()
     })
 
     it('should handle empty file list', async () => {
-      const dataTransfer = new DataTransfer()
-      await expect(app.handleFileList(dataTransfer.files)).rejects.toThrow()
+      await expect(app.handleFileList([])).rejects.toThrow()
     })
 
     it('should not process unsupported file types', async () => {
       const invalidFile = createTestFile('test.pdf', 'application/pdf')
-      const dataTransfer = new DataTransfer()
-      dataTransfer.items.add(invalidFile)
 
-      await app.handleFileList(dataTransfer.files)
+      await app.handleFileList([invalidFile])
 
       expect(pasteImageNodes).not.toHaveBeenCalled()
       expect(createNode).not.toHaveBeenCalled()