Feat: early mouse support

src/services/help_nav.rs

@@ -8,6 +8,12 @@ pub fn toggle_focus(ui: &mut UiState) {
     };
 }
 
+pub fn select_topic(ui: &mut UiState, index: usize) {
+    if index < docs::topic_count() {
+        ui.help_topic = index;
+    }
+}
+
 pub fn next_topic(ui: &mut UiState, n: usize) {
     let count = docs::topic_count();
     ui.help_topic = (ui.help_topic + n) % count;