FIX:microsoft word text copy and paste error

[ShadowJobs]

Summary

Fix #15674
Fixes: This addresses a newly identified bug。
Addresses unexpected file validation when pasting text from Microsoft Word, where clipboard metadata caused false-positive "文件类型不支持" errors. （Only Microsoft Word has this issue; WPS does not.）

• Root cause:
  Microsoft Word's clipboard operation injects file metadata alongside text content. During pasting:
• e.clipboardData.files and e.clipboardData.items both contain data
• The original handleClipboardPasteFile() logic prioritized checking files[0] existence
• This caused text pasting to be incorrectly intercepted as file upload attempts

Technical breakdown:

// Problematic logic
const file = e.clipboardData?.files[0]
if (file) {  // ← MS Word satisfies this
  handleFileUpload()             // ← Wrong execution path
  e.preventDefault()             // ← Blocks default text paste
}

Solution:

• Modified handleClipboardPasteFile to check for simultaneous text presence
• Only trigger file upload when:
  • Clipboard contains a file
  • AND no plain text exists in clipboard data

Technical Details

Updated validation logic:

const handleClipboardPasteFile = useCallback((e: ClipboardEvent<HTMLTextAreaElement>) => {
  const file = e.clipboardData?.files[0]
  const text = e.clipboardData?.getData('text/plain') // New text check
  if (file && !text) { // Critical condition update
    e.preventDefault()
    handleLocalFileUpload(file)
  }
}, [handleLocalFileUpload])

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods