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/grid.rs

@@ -448,7 +448,7 @@ fn wire_grid_sync_and_load(window: &AppWindow, ctl: &Rc<LibraryController>) {
     {
         let weak = window.as_weak();
         let ctl = ctl.clone();
-        window.on_library_sync_now(move || {
+        window.global::<Library>().on_library_sync_now(move || {
             if let Some(w) = weak.upgrade() {
                 start_derived_sync(&w, &ctl);
             }
@@ -461,11 +461,13 @@ fn wire_grid_sync_and_load(window: &AppWindow, ctl: &Rc<LibraryController>) {
     {
         let weak = window.as_weak();
         let ctl = ctl.clone();
-        window.on_library_thumbnail_all(move || {
-            if let Some(w) = weak.upgrade() {
-                start_thumbnail_sweep(&w, &ctl);
-            }
-        });
+        window
+            .global::<Library>()
+            .on_library_thumbnail_all(move || {
+                if let Some(w) = weak.upgrade() {
+                    start_thumbnail_sweep(&w, &ctl);
+                }
+            });
     }
 
     // A column-count change moves which cells begin a row, and month headings
@@ -666,7 +668,7 @@ fn wire_grid_routes(
     // folder could not be changed without clearing stored state by hand.
     {
         let weak = window.as_weak();
-        window.on_library_change(move || {
+        window.global::<Library>().on_library_change(move || {
             if let Some(w) = weak.upgrade() {
                 w.set_active_view(View::Launch);
             }
@@ -715,7 +717,7 @@ fn wire_grid_routes(
         let weak = window.as_weak();
         let ctl = ctl.clone();
         let coll_ctl = coll_ctl.clone();
-        window.on_library_rescan(move || {
+        window.global::<Library>().on_library_rescan(move || {
             let Some(w) = weak.upgrade() else { return };
             start_rescan(&w, &ctl, &coll_ctl);
         });