fix(mqtt): clear legacy prefs, restore status publishing, and expand web controls

variants/eastmesh_mqtt/platformio.ini

@@ -464,6 +464,7 @@ build_flags =
   -D WIFI_PWD='"mypwd"'
   -D MQTT_DEFAULT_IATA='"MEL"'
   -D CONFIG_MBEDTLS_CERTIFICATE_BUNDLE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
 build_src_filter = ${heltec_v4_oled.build_src_filter}
   +<helpers/mqtt/*.cpp>
   +<helpers/ui/SSD1306Display.cpp>