Honor saved WebUI off during unconfigured boot setup

An enabled MQTT bridge without a saved SSID forced WebConfig back on at boot,
even after set webui off. Its setup AP also suspended an enabled ESP-NOW bridge.

Use first-time MQTT setup as the default only when no WebUI choice is saved.
Apply the saved on/off setting afterward in Repeater and Room Server. Preserve
first-time provisioning and explicit starts.

Add executable boot regressions for both roles with unset, on and off WebUI
settings and configured/unconfigured WiFi. Update setup and picker guidance.

examples/simple_room_server/MyMesh.cpp

@@ -2828,10 +2828,14 @@ void MyMesh::begin(FILESYSTEM *fs) {
 #endif
 
 #if defined(WITH_WEBCONFIG) && !defined(WEBCONFIG_NO_AUTO_AP)
-  bool start_webui = WebConfigServer::loadEnabled(false);
+  bool start_webui = false;
+#ifdef WITH_MQTT_BRIDGE
+  // First-boot MQTT setup is a default, never an override of saved WebUI off.
+  start_webui = _prefs.bridge_enabled
+      && !WebConfigServer::hasConfiguredWiFi(_cli.getObserverPrefs());
+#endif
+  start_webui = WebConfigServer::loadEnabled(start_webui);
 #ifdef WITH_MQTT_BRIDGE
-  start_webui = start_webui || (_prefs.bridge_enabled
-      && !WebConfigServer::hasConfiguredWiFi(_cli.getObserverPrefs()));
   if (start_webui && !WebConfigServer::hasConfiguredWiFi(_cli.getObserverPrefs())) {
 #if defined(WITH_ESPNOW_BRIDGE)
     if (espnow_bridge.isRunning()) espnow_bridge.end();