Add Linux BLE pairing helper that drives bluetoothctl for pair/trust/PIN
entry, with Completer-based flow control, explicit retry loop, and named
timeout constants.
- LinuxBlePairingService: pair-and-trust with up to 2 retries
- LinuxBleErrorClassifier: map bluetoothctl stderr to user-facing errors
- Conditional import stub for web builds (dart.library.io gate)
- Scanner screen: PIN dialog integration for Linux pairing flow
- MeshCoreConnector: Linux pairing/recovery/reconnect wiring
- l10n: 4 new pairing keys across all 14 locales
- 12 unit tests (pairing service + error classifier)
just-stuff-tm
29660d520e