Desktop: Fix adding tags to a note through drag-and-drop

[personalizedrefrigerator]

Summary

This pull request adds a previously-missing property to tag items in the tag list. This missing property prevented assigning tags through drag-and-drop from working.

See the issue report on the forum for details.

Testing plan

Fedora 41 Linux:

1. Create a new note.
2. Drag the note from the note list to a tag in the tag list.
3. Drop the note.
4. Verify that the note is now associated with the tag from step 2.