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/library_ui/window.rs

@@ -234,13 +234,15 @@ pub(super) fn load_window(window: &AppWindow, ctl: &Rc<LibraryController>) {
     // Three queries deep — descendants, their images, and whether every one of
     // them is pinned — and the answer cannot change by scrolling.
     if describes_something_new {
-        window.set_library_scope_pinned(match scope {
-            Some(id) => dr_catalog::collections::descendants(catalog.connection(), id)
-                .map(|ids| collection_images(catalog, &ids))
-                .map(|images| scope_is_pinned(catalog, &images))
-                .unwrap_or(false),
-            None => false,
-        });
+        window
+            .global::<Library>()
+            .set_library_scope_pinned(match scope {
+                Some(id) => dr_catalog::collections::descendants(catalog.connection(), id)
+                    .map(|ids| collection_images(catalog, &ids))
+                    .map(|images| scope_is_pinned(catalog, &images))
+                    .unwrap_or(false),
+                None => false,
+            });
     }
     // Read before it is overwritten: the property still holds what the library
     // was last time this ran, and a library that has become shorter is the
@@ -293,7 +295,9 @@ pub(super) fn load_window(window: &AppWindow, ctl: &Rc<LibraryController>) {
     let cells = match cells {
         Ok(c) => c,
         Err(e) => {
-            window.set_library_error(format!("reading catalog: {e}").into());
+            window
+                .global::<Library>()
+                .set_library_error(format!("reading catalog: {e}").into());
             return;
         }
     };
@@ -757,7 +761,7 @@ fn drain_thumbnails(
                         if !parts.is_empty() {
                             let status = parts.join(" · ");
                             job.detail(status.clone());
-                            w.set_library_status(status.into());
+                            w.global::<Library>().set_library_status(status.into());
                         }
                     }
                     // A header-only date read. Advances the bar; draws nothing.