[Feature]: Implement duplicate source detection and warning system

Feature Description

Currently, users can add new sources to Open Notebook by uploading documents or providing links. However, there is no mechanism to detect if a source already exists in the system. This can lead to duplicate entries, especially as the number of sources grows.

It would be usefull to implement a duplicate source warning system.

Proposed behavior:

• When a user attempts to upload a document or add a link as a new source, the system checks if that source already exists (e.g., based on file name, document hash, or link URL).
• If a duplicate is found, display a warning message informing the user that the source already exists.
• The user can then choose to:
  • Cancel the upload, or
  • Proceed anyway (in case the duplicate is intentional).

Why would this be helpful?

This feature would help keep the system organized and prevent duplicate sources. It ensures cleaner data management, reduces redundancy, and improves user experience as the number of sources increases.

Proposed Solution (Optional)

No response

Additional Context

No Additional Context

Contribution

• I am a developer and would like to work on implementing this feature (pending maintainer approval)