fix(core,fuse,gui): UI/UX quick wins from the audit (phase 0)

- Move Google Takeout import out of Settings; Photos owns it, and the
  Takeout page's back button returns there.
- Trash from the file browser is Undo-only (no confirm); F2 on a
  multi-selection explains why it does nothing.
- Ask before sign-out, rejecting an invitation, removing someone's access,
  removing a public link, and switching a folder to on-demand.
- Clearer offline wording ("Make available offline" / "Make online only")
  with dedicated offline, online-only and upload symbolic icons; the pin row
  is hidden for folders.
- Search hits report whether a file is cached, so search results show the
  offline badge.
- Activity log: readable Empty Trash / link entries, distinct icons, and
  error/warning styling for failures and conflicts.
- Proper singular/plural counts instead of "item(s)" / "archive(s)".
- Name earlier versions by save time instead of revision id; capitalise
  the public link role; stop-syncing uses a stop icon, not a trash can.
- Label the Photos Upload and "Show on map" buttons; toast when a
  thumbnail build finishes; the versions button follows the mount state.
- Mode switches and device mutations reload both sync pages.

crates/pdfs-gui/src/app/pages/trash.rs

@@ -378,7 +378,8 @@ pub(crate) fn prompt_empty_trash(ui: &Rc<Ui>) {
     let dialog = adw::AlertDialog::builder()
         .heading("Empty Trash")
         .body(format!(
-            "Permanently delete all {count} item(s) in the trash? This cannot be undone."
+            "Permanently delete all {} in the trash? This cannot be undone.",
+            count_noun(count as usize, "item", "items")
         ))
         .build();
     dialog.add_response("cancel", "Cancel");