fix(fuse,core,cli,gui): show a refused session as expired, not offline

A refresh token Proton refused, or a deleted or disabled account, was
treated as a lost connection: the mount came up "offline", the probe
retried forever and logged only at debug, and nothing told the user that
only signing in again helps (issue #35).

session_revoked() names those errors. The root fetch, probe, drain,
event poll, event seed and photos root now set session_expired, log one
warning naming `pdfs login`, and stop retrying. Cached files stay
readable and changes stay queued.

Response::Status carries session_expired (serde default false). The
tray shows "Session expired — sign in again" with a Sign In Again…
item that opens the app's sign-in page; the app's status and Sync card
say the same with a button. `pdfs status` and `pdfs diagnose` report it.
New strings are translated in every catalog.

docs/BUGS.md B202.

crates/pdfs-gui/src/app/main.rs

@@ -579,6 +579,7 @@ fn build_window(app: &adw::Application) {
                 detail: locations_widgets.card_detail.clone(),
                 pause: locations_widgets.pause.clone(),
                 paused: Cell::new(false),
+                sign_in: locations_widgets.card_sign_in.clone(),
             },
             queue: QueueState {
                 group: locations_widgets.queue_group.clone(),
@@ -1290,6 +1291,12 @@ fn install_launch_actions(ui: &Rc<Ui>, app: &adw::Application, window: &adw::App
         if ui_page.session.borrow().is_none() {
             return;
         }
+        // Signed in, but Proton refused the session (the tray's "Sign In
+        // Again…"): the login page, with the rest of the app still reachable.
+        if page == "login" {
+            show_login(&ui_page);
+            return;
+        }
         // Activity lives on as the Sync page's History view.
         if page == "activity" {
             ui_page.locations.views.set_visible_child_name("history");