help: the search block's (i) on its header, a 12 px mark, and a real search page

src/ui_trigger.cpp

@@ -599,6 +599,11 @@ GtkWidget* build_trigger_panel(App& app) {
   app.search_pos_label = GTK_WIDGET(gtk_builder_get_object(ui, "search_pos"));
   app.search_next_button = GTK_WIDGET(gtk_builder_get_object(ui, "search_next"));
   app.search_marks_label = GTK_WIDGET(gtk_builder_get_object(ui, "search_marks"));
+  app.search_exp = GTK_WIDGET(gtk_builder_get_object(ui, "search_exp"));
+  // The expander's header box, where the contextual help's "trigger_search" hint joins as its last
+  // child (see `ui_context_help.cpp`): a hint on the block's own child would leave it unreachable
+  // while the block is collapsed.
+  app.trigger_search = GTK_WIDGET(gtk_builder_get_object(ui, "search_head"));
   if (app.search_run_button != nullptr) {
     g_signal_connect(app.search_run_button, "clicked", G_CALLBACK(+[](GtkButton*, gpointer user) {
                        App* a = static_cast<App*>(user);