Preferences (File menu): theme, grid, perspective, auto-project face edges, body selection; all kept between runs

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/ui-egui/src/toolbar.rs

@@ -159,6 +159,10 @@ fn file_menu(app: &mut SolveApp, ctx: &egui::Context) {
                 close = true;
             }
             ui.separator();
+            if item(ui, "Preferences…", "") {
+                app.dialog = Some(crate::dialogs::Dialog::preferences());
+                close = true;
+            }
             if item(ui, "Quit", "") {
                 app.quit_requested = true;
                 close = true;