Title screen: licence line and a link to the repository at the bottom

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main.rs

@@ -678,6 +678,7 @@ async fn main() {
                         ui.show_help = false;
                         autosave_t = 0.0;
                     }
+                    MenuAction::OpenRepo => platform::open_url(menu::REPO_URL),
                     MenuAction::EditName => {
                         if let Some(n) = platform::prompt(&i18n::tr("saves.name"), &menu.save_name) {
                             menu.save_name = n.chars().filter(|c| !c.is_control()).take(40).collect();