refactor(companion): the app's links through upstream's MultiSerialInterface

- Bluetooth + USB (+ WiFi/Ethernet/UART per build) in one interface_manager,
  as upstream; frames go to every enabled link, USB is read while BT is
  connected. DUAL_SERIAL now means ENABLE_USB_INTERFACE.
- WiFi interface with upstream's wifi_* prefs and set/get wifi.* CLI.
- isClientConnected moved into ArduinoSerialInterface (DTR on nRF52 and
  ESP32 native CDC).
- UI uses isBluetoothEnabled/enableBluetooth/disableBluetooth; turning BT
  off leaves USB and the other links on.
- DualSerialInterface removed.
- Sim build gains DynamicConfigSerializer.cpp (broken since bd64c203).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/companion_radio/ui-lvgl/UITask.h

@@ -7,7 +7,7 @@
 #include <Arduino.h>
 #include <helpers/ui/DisplayDriver.h>
 #include <helpers/SensorManager.h>
-#include <helpers/BaseSerialInterface.h>
+#include <helpers/MultiSerialInterface.h>
 #include <lvgl.h>
 // A big zero-initialised static in PSRAM (ESP32): the internal RAM is what
 // WiFi starts and joins on. Not for what DMA or an interrupt touches.
@@ -53,7 +53,7 @@ struct TextEntry {
 
 class UITask : public UITaskBase, public UiCoreHost {
 public:
-  UITask(mesh::MainBoard* board, BaseSerialInterface* serial) : UITaskBase(board, serial) {}
+  UITask(mesh::MainBoard* board, MultiSerialInterface* serial) : UITaskBase(board, serial) {}
 
   void begin(DisplayDriver* display, SensorManager* sensors, NodePrefs* node_prefs);
   void loop() override;