Feature Request: Drag & drop text files to populate paste content (like GitHub Gists)

Feature Description

Add support for dragging and dropping text files directly onto the PrivateBin editor to automatically populate the paste content with the file's contents, similar to how GitHub Gists works.

Current Behavior

When dragging a text file onto PrivateBin:

• If file upload is disabled: Browser opens the file in a new tab
• If file upload is enabled: File is attached as an attachment to the paste

Desired Behavior

When dragging a text file onto the PrivateBin editor:

• The content of the text file should be inserted into the paste editor
• This would work similar to GitHub Gists' drag & drop functionality
• The file itself would not be attached, just its content would populate the editor

Use Case

This feature would streamline the workflow for users who want to quickly share text file contents without:

1. Opening the file
2. Copying the content
3. Pasting it into PrivateBin

Instead, they could simply drag the file and have its content automatically populate the paste.

Distinction from Current File Upload

This is different from the existing file upload/attachment feature:

• Current feature: Attaches files as separate attachments to a paste
• Requested feature: Reads text file content and inserts it into the paste editor itself

Both features could coexist:

• Text files could populate the editor content
• Binary files (images, PDFs, etc.) could still be attached as attachments

Reference

Original discussion: https://github.com/orgs/PrivateBin/discussions/1656#discussioncomment-14607195