Setting to remove unlinked attachments

Add a button in settings to remove orphan attachments (in database but not linked to an entry)

Start by locating the settings screen and the attachment storage/database code. Trace how attachments are linked to entries, then define the cleanup behavior so the settings button removes only orphan attachments while preserving linked ones; verify the result with the project's relevant tests.

Written by the indexing model from the issue text.