Give the collections sidebar its own Slint global

AppWindow carried the sidebar's tree, its row menu, renaming, drag and
drop between rows, the trash row, and the membership sheet as ~40
properties and callbacks on the root component, in the pattern CH-1
describes and the develop screen's globals (Adjustments, Framing, Steps,
...) already replaced. Collections.* in collections.slint now holds that
state, declared next to the MembershipRow struct it and the membership
sheet both use; Rust reaches it through window.global::<Collections>()
instead of window.set_/get_/on_/invoke_ on the root.

collection-selected, collection-select, and collection-offline-menu stay
on AppWindow: library_ui.rs invokes collection-select directly and
registers collection-offline-menu's handler, and lib.rs reads
collection-selected for back-navigation, so moving them would have meant
editing library_ui.rs, which another change on this branch is splitting
into a module directory. collections-visible stays too — it is
lib.rs's panel-layout state, seeded from the saved layout before the
sidebar exists, and collections_ui never touches it. Everything prefixed
library- (the grid's drag, selection and keyword state that the sidebar's
Rust also wires for cross-feature gestures like filing a selection into
a collection) stays on the window as well, since it belongs to the
library screen, not the sidebar.

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

@@ -12,7 +12,7 @@ use dr_catalog::Catalog;
 use dr_types::ImageId;
 use slint::ComponentHandle;
 
-use crate::AppWindow;
+use crate::{AppWindow, Collections};
 
 use super::controller::CollectionsController;
 use super::tree_sync::refresh_tree;
@@ -31,7 +31,9 @@ pub(super) fn start_trash(
     reload: &Rc<dyn Fn()>,
 ) {
     let Some(conn) = session() else {
-        window.set_collection_error("Open a library first.".into());
+        window
+            .global::<Collections>()
+            .set_collection_error("Open a library first.".into());
         return;
     };
 
@@ -41,7 +43,9 @@ pub(super) fn start_trash(
         match crate::trash::plan_trash(cat, &conn.account.root, images) {
             Ok(m) => m,
             Err(e) => {
-                window.set_collection_error(format!("planning delete: {e}").into());
+                window
+                    .global::<Collections>()
+                    .set_collection_error(format!("planning delete: {e}").into());
                 return;
             }
         }
@@ -97,7 +101,9 @@ pub(super) fn start_restore(
     reload: &Rc<dyn Fn()>,
 ) {
     let Some(conn) = session() else {
-        window.set_collection_error("Open a library first.".into());
+        window
+            .global::<Collections>()
+            .set_collection_error("Open a library first.".into());
         return;
     };
 
@@ -107,7 +113,9 @@ pub(super) fn start_restore(
         match crate::trash::plan_restore(cat, images) {
             Ok(m) => m,
             Err(e) => {
-                window.set_collection_error(format!("planning restore: {e}").into());
+                window
+                    .global::<Collections>()
+                    .set_collection_error(format!("planning restore: {e}").into());
                 return;
             }
         }
@@ -116,7 +124,7 @@ pub(super) fn start_restore(
     if moves.is_empty() {
         // Said out loud rather than passed over in silence: a button that does
         // nothing visible reads as broken, and the reason here is specific.
-        window.set_collection_error(
+        window.global::<Collections>().set_collection_error(
             "Nothing to restore — no record of where these came from.".into(),
         );
         return;
@@ -227,7 +235,8 @@ pub(super) fn drain_trash(
                         }
                         w.set_library_status(status.into());
                         if let Some(first) = failed.first() {
-                            w.set_collection_error(first.as_str().into());
+                            w.global::<Collections>()
+                                .set_collection_error(first.as_str().into());
                         }
 
                         let borrow = catalog.borrow();
@@ -264,8 +273,8 @@ fn stop_trash(ctl: &Rc<CollectionsController>) {
 /// it.
 pub fn refresh_trash(window: &AppWindow, catalog: &Catalog) {
     let (n, bytes) = dr_catalog::trash::summary(catalog.connection()).unwrap_or((0, 0));
-    window.set_trash_count(n as i32);
-    window.set_trash_label(if n == 0 {
+    window.global::<Collections>().set_trash_count(n as i32);
+    window.global::<Collections>().set_trash_label(if n == 0 {
         slint::SharedString::new()
     } else {
         format!("{n} · {}", format_bytes(bytes)).into()