Refine USB transport flow

- replace Android USB dependency with app-owned USB host implementation\n- restore BLE-first scanner flow with USB secondary action\n- tighten Web Serial key handling and disconnect logging\n\nTODO (follow-up):\n- review non-English localization copy for tone and consistency\n- trim remaining unused/awkward localization strings introduced during USB UI changes

lib/l10n/app_en.arb

@@ -1,4 +1,4 @@
-{
+{
   "@@locale": "en",
   "appTitle": "MeshCore Open",
   "nav_contacts": "Contacts",
@@ -28,7 +28,7 @@
   "common_disable": "Disable",
   "common_reboot": "Reboot",
   "common_loading": "Loading...",
-  "common_notAvailable": "—",
+  "common_notAvailable": "—",
   "common_voltageValue": "{volts} V",
   "@common_voltageValue": {
     "placeholders": {
@@ -46,8 +46,6 @@
     }
   },
   "scanner_title": "MeshCore Open",
-  "connectionChoiceTitle": "Choose your connection method",
-  "connectionChoiceSubtitle": "Select how you would like to reach your MeshCore device.",
   "connectionChoiceUsbLabel": "USB",
   "connectionChoiceBluetoothLabel": "Bluetooth",
   "usbScreenTitle": "Connect over USB",
@@ -180,20 +178,20 @@
   "appSettings_language": "Language",
   "appSettings_languageSystem": "System default",
   "appSettings_languageEn": "English",
-  "appSettings_languageFr": "Français",
-  "appSettings_languageEs": "Español",
+  "appSettings_languageFr": "Français",
+  "appSettings_languageEs": "Español",
   "appSettings_languageDe": "Deutsch",
   "appSettings_languagePl": "Polski",
-  "appSettings_languageSl": "Slovenščina",
-  "appSettings_languagePt": "Português",
+  "appSettings_languageSl": "Slovenščina",
+  "appSettings_languagePt": "Português",
   "appSettings_languageIt": "Italiano",
-  "appSettings_languageZh": "中文",
+  "appSettings_languageZh": "中文",
   "appSettings_languageSv": "Svenska",
   "appSettings_languageNl": "Nederlands",
-  "appSettings_languageSk": "Slovenčina",
-  "appSettings_languageBg": "Български",
-  "appSettings_languageRu": "Русский",
-  "appSettings_languageUk": "Українська",
+  "appSettings_languageSk": "Slovenčina",
+  "appSettings_languageBg": "Български",
+  "appSettings_languageRu": "Русский",
+  "appSettings_languageUk": "Українська",
   "appSettings_enableMessageTracing": "Enable Message Tracing",
   "appSettings_enableMessageTracingSubtitle": "Show detailed routing and timing metadata for messages",
   "appSettings_notifications": "Notifications",
@@ -1341,7 +1339,7 @@
       }
     }
   },
-  "telemetry_temperatureValue": "{celsius}°C / {fahrenheit}°F",
+  "telemetry_temperatureValue": "{celsius}°C / {fahrenheit}°F",
   "@telemetry_temperatureValue": {
     "placeholders": {
       "celsius": {
@@ -1391,7 +1389,7 @@
   "channelPath_repeatsLabel": "Repeats",
   "channelPath_pathLabel": "Path {index}",
   "channelPath_observedLabel": "Observed",
-  "channelPath_observedPathTitle": "Observed path {index} • {hops}",
+  "channelPath_observedPathTitle": "Observed path {index} • {hops}",
   "@channelPath_observedPathTitle": {
     "placeholders": {
       "index": {
@@ -1466,7 +1464,7 @@
   },
   "channelPath_pathLabelTitle": "Path",
   "channelPath_observedPathHeader": "Observed Path",
-  "channelPath_selectedPathLabel": "{label} • {prefixes}",
+  "channelPath_selectedPathLabel": "{label} • {prefixes}",
   "@channelPath_selectedPathLabel": {
     "placeholders": {
       "label": {