When starting JabRef, and creating an empty library, there is no content in the entry table:

Task:

• Create button "Add example entry", which adds the BibEntry shown at https://github.com/jabref/jabref/?tab=readme-ov-file#research-and-education.
• Create button "Import your existing PDFs", which i) ensures that the library directory exists (*) and ii) trigger "Lookup" > "Search for unlinked files" afterwards. In case there is no library directory, ask the user to configure one: Show a notification that no directory exist and then open the library properties.

Note: This is not about JabRef showing no library at all.

(*) Check if org.jabref.model.database.BibDatabaseContext#getFileDirectories is non-empty