Remove the SETUP card: the browser tree shows the progress

The setup checklist card (#265), its show_setup view setting, the View
menu checkbox and the preferences file that only remembered it go; the
tree's marks and ghost rows replace them. Session::progress and
model.check's progress stay for agents. An old prefs.json is no longer
read.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/ui-egui/src/viewport.rs

@@ -559,7 +559,6 @@ fn nav_bar(app: &mut ModelApp, ui: &mut egui::Ui, rect: Rect, t: &Tokens) {
             ui.checkbox(&mut app.ui.show_interactions, "Interactions");
             ui.separator();
             ui.checkbox(&mut app.ui.show_tree, "Browser");
-            ui.checkbox(&mut app.ui.show_setup, "Setup checklist");
             ui.checkbox(&mut app.ui.show_timeline, "Timeline");
         });
     }