fix: correct dual serial interface — routing, UI state, debug logging

- isConnected() returns true always (USB always available, mesh can send)
- isBLEConnected() added to BaseSerialInterface for BLE-specific UI/buzzer state
- MyMesh uses isBLEConnected() to update UITask connection indicator
- Disable BLE_DEBUG_LOGGING in dual build (would corrupt USB stream)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

variants/wio-tracker-l1/platformio.ini

@@ -140,6 +140,7 @@ extra_scripts = post:create-uf2.py
 extends = WioTrackerL1CompanionBLE
 build_flags = ${WioTrackerL1CompanionBLE.build_flags}
   -D DUAL_SERIAL=1
+  -U BLE_DEBUG_LOGGING
 
 [env:WioTrackerL1_companion_radio_dual]
 extends = WioTrackerL1CompanionDual