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-core/src/control.rs

@@ -976,6 +976,10 @@ pub struct SearchHit {
     pub size: u64,
     pub modified: i64,
     pub pinned: bool,
+    /// Whether a valid copy of the content is in the local cache. Legacy
+    /// daemons omit it; clients then treat the file as online-only.
+    #[serde(default)]
+    pub cached: bool,
     /// Node uid in `volume~link` form.
     pub uid: String,
     /// Absolute path through the most specific active on-demand mount, when the
@@ -2133,6 +2137,7 @@ mod tests {
                 size: 12,
                 modified: 123,
                 pinned: true,
+                cached: false,
                 uid: "vol~link".into(),
                 mounted_path: Some("/home/me/Videos/report.pdf".into()),
                 score: 985,