Feature Request: use existing document type

[Anaxagoras-bc]

Try and reuse existing document types based on what exists in paperless-ngx, rather than having to manually enter the document types into the prompt. Paperless-AI should pull the list of document types from paperless-ngx similar to how it does so for tags and correspondents and then paperless-ai prompt's the llm with the existing list of tags and correspondants in paperless-ngx.

[Fact0ryy]

+1. Please add an option to "Restrict to Existing Document Types" under AI Restrictions.

This would ensure that Paperless-AI doesn't suggest or create new document types outside the predefined list, similar to how it already handles tags and correspondents. It would help maintain a clean and consistent set of document types – especially in environments where strict classification rules are required.

Thanks for your great work!