Add Bluetooth permission and adapter state handling for Android and iOS

lib/services/ble_client.dart

@@ -8,6 +8,8 @@ import 'protocol_log.dart';
 
 enum BleConnectionState { disconnected, connected }
 
+enum BleAdapterState { unknown, unsupported, off, on, unauthorized }
+
 /// Thin boundary between OpenScooter and the underlying BLE plugin.
 ///
 /// OpenScooter v1 supports EXACTLY ONE active scooter connection at a time.
@@ -17,6 +19,13 @@ enum BleConnectionState { disconnected, connected }
 /// Protocol code never imports the BLE plugin directly, so protocol tests run
 /// with `flutter test` and a fake subclass, without hardware.
 abstract class BleClient {
+  /// Current Bluetooth adapter state, emitting on change. Fakes default to on.
+  Stream<BleAdapterState> get adapterState => Stream.value(BleAdapterState.on);
+
+  /// Asks the OS to enable Bluetooth. Only Android supports this; elsewhere it
+  /// is a no-op and the UI must direct the user to system settings.
+  Future<void> turnOn() async {}
+
   /// Streams the current set of visible devices. Scanning starts on listen
   /// and stops when the subscription is cancelled.
   Stream<List<ScooterDevice>> scan();
@@ -63,6 +72,27 @@ class FlutterBleClient extends BleClient {
   @override
   Stream<BleConnectionState> get connectionState => _connState.stream;
 
+  @override
+  Stream<BleAdapterState> get adapterState =>
+      fbp.FlutterBluePlus.adapterState.map((s) => switch (s) {
+            fbp.BluetoothAdapterState.on => BleAdapterState.on,
+            fbp.BluetoothAdapterState.off ||
+            fbp.BluetoothAdapterState.turningOff ||
+            fbp.BluetoothAdapterState.turningOn =>
+              BleAdapterState.off,
+            fbp.BluetoothAdapterState.unauthorized => BleAdapterState.unauthorized,
+            fbp.BluetoothAdapterState.unavailable => BleAdapterState.unsupported,
+            fbp.BluetoothAdapterState.unknown => BleAdapterState.unknown,
+          });
+
+  @override
+  Future<void> turnOn() async {
+    if (defaultTargetPlatform == TargetPlatform.android) {
+      _log('ADAPTER turnOn requested');
+      await fbp.FlutterBluePlus.turnOn();
+    }
+  }
+
   @override
   Stream<List<ScooterDevice>> scan() {
     late StreamController<List<ScooterDevice>> controller;
@@ -70,12 +100,7 @@ class FlutterBleClient extends BleClient {
 
     Future<void> start() async {
       try {
-        var adapter = await fbp.FlutterBluePlus.adapterState.first;
-        if (adapter != fbp.BluetoothAdapterState.on &&
-            defaultTargetPlatform == TargetPlatform.android) {
-          await fbp.FlutterBluePlus.turnOn();
-        }
-        adapter = await fbp.FlutterBluePlus.adapterState
+        await fbp.FlutterBluePlus.adapterState
             .where((s) => s == fbp.BluetoothAdapterState.on)
             .first
             .timeout(const Duration(seconds: 10));