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-new/HomeScreen.h

@@ -328,7 +328,7 @@ class HomeScreen : public UIScreen {
       add("All messages", Q_MORE, QA_MORE, 0);
       n += recentChats(rows + n, quickFit() - 1);
     } else if (page == BLUETOOTH) {
-      const bool on = _task->isSerialEnabled();
+      const bool on = _task->isBluetoothEnabled();
       add("Bluetooth", Q_SWITCH, QA_BT, on ? 1 : 0);
       add("Phone", Q_VALUE, QA_NONE, 0);
       char* v = rows[n - 1].value;
@@ -440,7 +440,7 @@ class HomeScreen : public UIScreen {
       case QA_BRIGHTNESS:
       case QA_AUTO_ADVERT: _quick_edit = true; break;   // Left/Right change it, Enter / Back keep it
       case QA_BT:
-        if (_task->isSerialEnabled()) _task->disableSerial(); else _task->enableSerial();
+        if (_task->isBluetoothEnabled()) _task->disableBluetooth(); else _task->enableBluetooth();
         break;
       case QA_ADVERT:
         _task->notify(UIEventType::ack);
@@ -609,7 +609,7 @@ class HomeScreen : public UIScreen {
     struct Sicon { bool active; const MiniIcon* icon; };
     const Sicon icons[] = {
       { board.isExternalPowered(),                                 &ICON_CHARGE },   // USB power: next to the battery
-      { _task->isSerialEnabled() && _task->isBLEConnected(),       &ICON_BLUETOOTH },
+      { _task->isBluetoothEnabled() && _task->isBLEConnected(),       &ICON_BLUETOOTH },
       { gps_on,                                                    gps_fix ? &ICON_GPS : &ICON_GPS_SEARCH },
       { _node_prefs && _node_prefs->alarm_on,                      &ICON_ALARM },
       { mute_on,                                                   &ICON_MUTE },