ui: one badge per enabled signal, an N signals overflow, and the order kept in memory

src/ui.cpp

@@ -4673,7 +4673,10 @@ void run_app_action(App& app, AppAction action) {
       toggle(app.cursors_toggle);
       break;
     case AppAction::ShowMeasure: dock_show_section(app, "measure"); break;
-    case AppAction::ShowSignals: slideover_toggle(app, "signals"); break;
+    case AppAction::ShowSignals:
+      // The `+` badge is insensitive without signals; so is its shortcut.
+      if (!app.model->signals().empty()) slideover_toggle(app, "signals");
+      break;
     case AppAction::LayoutEditor:
       toggle(app.layout_toggle);
       break;
@@ -5887,6 +5890,9 @@ int run_ui(int argc, char** argv, const Config& cfg, ScopeModel& model, Acquisit
   if (const char* env = g_getenv("UDPSCOPE_PROBE_BADGES_MS")) {
     g_timeout_add(static_cast<guint>(std::atoi(env)), badges_probe, &app);
   }
+  if (const char* env = g_getenv("UDPSCOPE_PROBE_SIGNAL_BADGES_MS")) {
+    g_timeout_add(static_cast<guint>(std::atoi(env)), signal_badges_probe, &app);
+  }
   if (const char* env = g_getenv("UDPSCOPE_PROBE_SIGNAL_PAGES_MS")) {
     g_timeout_add(static_cast<guint>(std::atoi(env)), signal_page_probe, &app);
   }