Sheet sets: reference menu order, new sheets stay closed, .dst reload, navigation fields

The tree menus follow the reference per row kind (New Sheet / Import on a
sheet work on its subset, Remove Subset only while empty, Rename Subset),
a new sheet is not opened, an open set reloads when its .dst changes on
disk, ViewportScale placeholders take the version of their format and
the codec pin moves to the revision with navigation fields.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/app/view/mod.rs

@@ -2644,6 +2644,16 @@ impl OpenCADStudio {
         };
         #[cfg(target_arch = "wasm32")]
         let plugin_drain = Subscription::none();
+        // Open sheet sets reload when their .dst changes on disk.
+        #[cfg(not(target_arch = "wasm32"))]
+        let sheet_set_poll = if self.sheet_set.sets.is_empty() {
+            Subscription::none()
+        } else {
+            iced::time::every(std::time::Duration::from_secs(1))
+                .map(|_| Message::SheetSet(crate::ui::window::sheet_set::SheetSetMsg::Poll))
+        };
+        #[cfg(target_arch = "wasm32")]
+        let sheet_set_poll = Subscription::none();
         let hatch_pattern_keys = if self.tabs[self.active_tab]
             .properties
             .hatch_pattern_picker_open
@@ -2845,6 +2855,7 @@ impl OpenCADStudio {
             web_fonts,
             autosave,
             plugin_drain,
+            sheet_set_poll,
             single_instance,
             hatch_pattern_keys,
             keyboard_events,