Move the library's routes and status onto its own Slint global

The scan/opening/status/error lines, offline mode and its retry, pinning a
collection offline, the sync and thumbnail-sweep state, and the callbacks
that route the grid to a rescan, a sync, another library, a panorama merge
or an export — the last of what AppWindow still carried under the
library- prefix — move onto the `Library` global started earlier on this
branch. Rust reaches them through window.global::<Library>() rather than
window.set_/get_/on_/invoke_ on the root.

library-visible is the one name that stays: it is computed from
active-page and active-view, the shell's own routing state, which a
global cannot read. AppWindow now declares no other library- property or
callback.

ui/dr-ui/src/recovery_ui.rs

@@ -44,7 +44,7 @@ use dr_catalog::recovery;
 use slint::ComponentHandle;
 
 use crate::library_ui::LibraryController;
-use crate::AppWindow;
+use crate::{AppWindow, Library};
 
 // What the open question is about.
 //
@@ -123,7 +123,7 @@ pub(crate) fn offer(window: &AppWindow, catalog: &Path, detail: &str) {
     window.set_recovery_busy(false);
     // The scan was held back, so the "Scanning…" the grid is showing behind
     // this would be a lie the moment the question is dismissed.
-    window.set_library_scanning(false);
+    window.global::<Library>().set_library_scanning(false);
 
     PENDING.with(|p| {
         *p.borrow_mut() = Some(Pending {
@@ -141,8 +141,8 @@ pub(crate) fn offer(window: &AppWindow, catalog: &Path, detail: &str) {
 fn dismiss(window: &AppWindow) {
     PENDING.with(|p| *p.borrow_mut() = None);
     window.set_recovery_title(slint::SharedString::new());
-    window.set_library_scanning(false);
-    window.set_library_error(
+    window.global::<Library>().set_library_scanning(false);
+    window.global::<Library>().set_library_error(
         "The library index is damaged. Rescan to rebuild it, or restore a backup.".into(),
     );
 }
@@ -243,7 +243,9 @@ fn answer(
 
     window.set_recovery_busy(false);
     window.set_recovery_title(slint::SharedString::new());
-    window.set_library_error(slint::SharedString::new());
+    window
+        .global::<Library>()
+        .set_library_error(slint::SharedString::new());
 
     if crate::library_ui::show_catalog_now(window, ctl, &pending.catalog, coll_ctl) {
         crate::library_ui::start_rescan(window, ctl, coll_ctl);