Preferences open over the Home page (#313)

The Home page returned from the frame before the Preferences window was
drawn, so the gear, Ctrl+, and Home's Preferences / Keyboard Shortcuts
links only set the flag and the dialog appeared after leaving Home.
Draw the Preferences window on Home too.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/ui-egui/src/lib.rs

@@ -978,6 +978,8 @@ impl SolveApp {
         if self.home.open {
             home::show(self, ui);
             if self.home.open {
+                // Preferences and Keyboard Shortcuts open from Home too (its links, the gear, Ctrl+,).
+                prefs::show(self, ui.ctx());
                 return;
             }
         }