feat(statusbar): isolate action menu on the pill and right-click

Clicking the ISO pill now opens a small menu with Isolate Objects, Hide
Objects and End Isolation instead of ending isolation directly; rows
that don't apply (no selection / nothing hidden) are dimmed. The same
actions are added to the viewport right-click menu.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/update.rs

@@ -1353,6 +1353,8 @@ impl OpenCADStudio {
                 // Close viewport context menu if open.
                 let i = self.active_tab;
                 self.tabs[i].scene.selection.borrow_mut().context_menu = None;
+                // Any command also dismisses the Isolate action menu.
+                self.isolate_popup_open = false;
                 self.dispatch_command(&cmd)
             }
 
@@ -3595,6 +3597,14 @@ impl OpenCADStudio {
                 self.tabs[i].dirty = true;
                 Task::none()
             }
+            Message::ToggleIsolatePopup => {
+                self.isolate_popup_open ^= true;
+                Task::none()
+            }
+            Message::CloseIsolatePopup => {
+                self.isolate_popup_open = false;
+                Task::none()
+            }
             Message::ToggleSnap(t) => {
                 self.snapper.toggle(t);
                 Task::none()