Refactor USB screen, add debug logging, fix UI issues

- Rewrite UsbScreen to mirror ScannerScreen patterns (status bar,
  tap-to-connect port list, bottom FABs, SnackBar errors)
- Extract MeshCoreUsbManager from MeshCoreConnector for cleaner
  USB transport ownership
- Add debug logging throughout USB connection flow (connector,
  manager, web/native services)
- Print debug logs to console in debug mode even when app debug
  log setting is disabled
- Localize remaining hardcoded strings (Web Serial Device fallback
  label, USB status bar keys, companion firmware timeout hint)
- Fix Swedish misspelling in translations (stöderliga → stödda)
- Guard Linux notification init against missing D-Bus session bus
- Fix SNRIndicator hit-test error by adding minimum size constraints
- Update USB flow tests for new UI patterns

lib/l10n/app_es.arb

@@ -1875,5 +1875,17 @@
   "usbErrorAlreadyActive": "La conexión USB ya está activa.",
   "usbErrorNoDeviceSelected": "No se ha seleccionado ningún dispositivo USB.",
   "usbErrorPortClosed": "La conexión USB no está activa.",
-  "usbErrorConnectTimedOut": "Se ha agotado el tiempo de espera mientras se esperaba la respuesta del dispositivo."
+  "usbFallbackDeviceName": "Dispositivo de serie web",
+  "@usbConnectionFailed": {
+    "placeholders": {
+      "error": {
+        "type": "String"
+      }
+    }
+  },
+  "usbStatus_connecting": "Conectándose al dispositivo USB...",
+  "usbStatus_searching": "Buscando dispositivos USB...",
+  "usbStatus_notConnected": "Seleccione un dispositivo USB",
+  "usbConnectionFailed": "Error al conectar mediante USB: {error}",
+  "usbErrorConnectTimedOut": "La conexión ha caducado. Asegúrese de que el dispositivo tenga el firmware USB Companion."
 }