concatenate multiline suggestions

this was mentioned in #16 but doesn't look like it's implemented yet.
Many papers have their titles split over multiple lines.
So it would be nice to also allow selecting multiple lines from the suggestions and concatenating them together as the new filename.

Look at the suggestion selection logic in the TUI, likely in a module handling user input and filename generation. The issue mentions concatenating multiple selected lines; examine how suggestions are currently processed and where multi-line selection would need to be integrated. Test with PDFs having multi-line titles to see the current behavior and verify the new feature works.

索引モデルが issue の本文から書いたものです。