Move the library grid's cells and selection onto their own Slint global

AppWindow carried the grid's loaded window of cells, the keyboard cursor,
drag and drop, the held-row long-press state, columns and cell size, the
scroll and viewport bookkeeping, the photo roll's pick and centre-request,
and the local-only/reorder/collection-filing gestures that act on a
selection, as properties and callbacks on the root component. That state now
lives in the `Library` global declared in library.slint, next to the structs
(LibraryCell, TimelineBar, KeywordRow, PersonChip) it and the grid's other
components already share; Rust reaches it through
window.global::<Library>() instead of window.set_/get_/on_/invoke_ on the
root, the same change collections.slint's `Collections` global made for the
sidebar.

library-visible stays on AppWindow: it is computed from active-page and
active-view, the shell's own routing state, which a global cannot read.
Everything else still prefixed library- — the timeline, the filter bar,
ratings and flags, keywording, and the routes and status lines — stays on
the window for now and moves in the commits that follow.

ui/dr-ui/src/collections_ui/tree_sync.rs

@@ -13,7 +13,7 @@ use dr_catalog::Catalog;
 use dr_types::{CollectionId, ImageId};
 use slint::{ComponentHandle as _, Model as _};
 
-use crate::{AppWindow, CollectionRow, Collections};
+use crate::{AppWindow, CollectionRow, Collections, Library};
 
 use super::controller::CollectionsController;
 
@@ -195,7 +195,7 @@ fn offline_state(
 /// Separate from [`sync_selection`] because the two differ: the selection
 /// persists after the drag, the lift lasts only while it is in flight.
 pub fn sync_lifted(window: &AppWindow, lifted: &[ImageId], ids: &[ImageId]) {
-    let model = window.get_library_cells();
+    let model = window.global::<Library>().get_library_cells();
     for (row, id) in ids.iter().enumerate() {
         let want = lifted.contains(id);
         if let Some(mut cell) = model.row_data(row) {
@@ -213,7 +213,7 @@ pub fn sync_lifted(window: &AppWindow, lifted: &[ImageId], ids: &[ImageId]) {
 /// this is what keeps the two in step after a scrub, a drop, or a click.
 pub fn sync_selection(window: &AppWindow, ctl: &Rc<CollectionsController>, ids: &[ImageId]) {
     let selection = ctl.selection.borrow();
-    let model = window.get_library_cells();
+    let model = window.global::<Library>().get_library_cells();
 
     // The anchor is deliberately **not** pushed to the grid.
     //
@@ -238,7 +238,9 @@ pub fn sync_selection(window: &AppWindow, ctl: &Rc<CollectionsController>, ids:
         }
     }
 
-    window.set_library_selected_count(selection.len() as i32);
+    window
+        .global::<Library>()
+        .set_library_selected_count(selection.len() as i32);
 }
 
 /// TRACES: FR-CAT-7
@@ -261,7 +263,7 @@ pub(super) fn sync_reorderable(window: &AppWindow) {
             .filter_map(|i| rows.row_data(i))
             .find(|r| r.id == id)
             .is_some_and(|r| !r.smart && !r.has_children);
-    window.set_library_reorderable(manual);
+    window.global::<Library>().set_library_reorderable(manual);
 }
 
 /// Refresh the per-cell "in this many collections" badges.
@@ -300,7 +302,7 @@ pub fn sync_badges(window: &AppWindow, catalog: &Catalog, ids: &[ImageId]) {
         }
     }
 
-    let model = window.get_library_cells();
+    let model = window.global::<Library>().get_library_cells();
     for (row, id) in ids.iter().enumerate() {
         let want = counts.get(&(id.0 as i64)).copied().unwrap_or(0);
         if let Some(mut cell) = model.row_data(row) {