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_sl.arb

@@ -1847,5 +1847,17 @@
   "usbErrorAlreadyActive": "USB povezava je že aktivirana.",
   "usbErrorNoDeviceSelected": "Ni bilo izbranega USB naprave.",
   "usbErrorPortClosed": "USB povezava ni aktivirana.",
-  "usbErrorConnectTimedOut": "Čakanje je preseglo določeno časovno obdobo, ker se naprave ni odzval."
+  "usbFallbackDeviceName": "Naprave za serijsko komunikacijo preko spleta",
+  "@usbConnectionFailed": {
+    "placeholders": {
+      "error": {
+        "type": "String"
+      }
+    }
+  },
+  "usbStatus_notConnected": "Izberite USB naprave.",
+  "usbStatus_connecting": "Povezava z USB napravo...",
+  "usbStatus_searching": "Iskanje USB naprav...",
+  "usbConnectionFailed": "Napaka pri povezavi preko USB: {error}",
+  "usbErrorConnectTimedOut": "Vzpostavitve ni bilo mogo. Prosimo, da se prepričate, da ima naprave trenutno nameštan firmware USB Companion."
 }