Add file type validation to paste upload

[halogen22]

Added checks to ensure pasted files match allowed types and uploader is enabled before proceeding. Displays an error notification if the file type is not supported.

Important

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2. Ensure there is an associated issue and you have been assigned to it
3. Use the correct syntax to link this PR: Fixes Allow image pasting upload only when file upload is enabled #27200 .

Summary

I fixed a bug that allowed pasting to succeed even when file uploads were disabled. While the original issue only described the problem with images, I found that pasting other file types was also possible. Therefore, I expanded the fix to cover all file types, not just images.

Screenshots

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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

[gemini-code-assist]

Summary of Changes

Hello @halogen22, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the security and user experience of the file upload component by introducing comprehensive validation for pasted files. It addresses a critical bug that allowed users to bypass upload restrictions by pasting files, ensuring that only permitted file types are processed and that the uploader's enabled state is respected. Users will now receive immediate feedback if their pasted file is not supported or if uploads are disabled.

Highlights

• File Type Validation: Implemented robust validation for pasted files, ensuring that only allowed file types are processed. This prevents unsupported files from being uploaded via the paste mechanism.
• Uploader Enabled Check: Added a check to verify if the file uploader is enabled before allowing any pasted file to proceed. This closes a bug where pasting could bypass the disabled state of the uploader.
• Error Notification: Introduced an error notification that informs the user immediately if a pasted file's type is not supported or if the file uploader is currently disabled.
• Expanded Scope: The fix was expanded to cover all file types, not just images, addressing a broader vulnerability where various file types could be pasted even when uploads were restricted.

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[gemini-code-assist]

Code Review

This pull request correctly adds a check to prevent file uploads via pasting when the feature is disabled, and also adds file type validation. My feedback focuses on removing redundant validation logic to improve code maintainability and points out an inconsistency with other upload methods like drag-and-drop to ensure consistent behavior across the application.

[crazywoola]

Please take a look at this comment.