feat: Add TCP connection support and UI integration

- Implemented TCP transport service for native platforms.
- Added TCP connection screen with input fields for host and port.
- Integrated TCP connection options into the scanner and USB screens.
- Updated localization files for new TCP-related strings.
- Added tests for TCP connection flow and error handling.
- Enhanced USB screen to include TCP connection option.
- Improved layout to ensure no overflow in narrow widths for scanner and USB screens.

test/services/tcp_transport_service_native_test.dart

@@ -0,0 +1,136 @@
+import 'dart:async';
+import 'dart:io';
+import 'dart:typed_data';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:meshcore_open/services/tcp_transport_service_native.dart';
+import 'package:meshcore_open/services/usb_serial_frame_codec.dart';
+
+final class _DelayedConnectOverrides extends IOOverrides {
+  _DelayedConnectOverrides(this.delay);
+
+  final Duration delay;
+
+  @override
+  Future<Socket> socketConnect(
+    host,
+    int port, {
+    sourceAddress,
+    int sourcePort = 0,
+    Duration? timeout,
+  }) async {
+    await Future<void>.delayed(delay);
+    return super.socketConnect(
+      host,
+      port,
+      sourceAddress: sourceAddress,
+      sourcePort: sourcePort,
+      timeout: timeout,
+    );
+  }
+}
+
+void main() {
+  test('connect/disconnect updates TCP transport state', () async {
+    final server = await ServerSocket.bind(InternetAddress.loopbackIPv4, 0);
+    final service = TcpTransportService();
+
+    try {
+      await service.connect(
+        host: InternetAddress.loopbackIPv4.address,
+        port: server.port,
+      );
+
+      expect(service.isConnected, isTrue);
+      expect(
+        service.activeEndpoint,
+        '${InternetAddress.loopbackIPv4.address}:${server.port}',
+      );
+
+      await service.disconnect();
+
+      expect(service.isConnected, isFalse);
+      expect(service.activeEndpoint, isNull);
+    } finally {
+      await service.disconnect();
+      await server.close();
+    }
+  });
+
+  test('disconnect is safe when already disconnected', () async {
+    final service = TcpTransportService();
+
+    await service.disconnect();
+    await service.disconnect();
+
+    expect(service.isConnected, isFalse);
+    expect(service.activeEndpoint, isNull);
+  });
+
+  test('emits only RX frames from socket stream', () async {
+    final server = await ServerSocket.bind(InternetAddress.loopbackIPv4, 0);
+    final acceptedSocket = Completer<Socket>();
+    final service = TcpTransportService();
+    final receivedFrames = <Uint8List>[];
+
+    final serverSub = server.listen((socket) {
+      if (!acceptedSocket.isCompleted) {
+        acceptedSocket.complete(socket);
+      } else {
+        socket.destroy();
+      }
+    });
+    final frameSub = service.frameStream.listen(receivedFrames.add);
+
+    try {
+      await service.connect(
+        host: InternetAddress.loopbackIPv4.address,
+        port: server.port,
+      );
+
+      final socket = await acceptedSocket.future.timeout(
+        const Duration(seconds: 2),
+      );
+
+      socket.add(<int>[usbSerialTxFrameStart, 0x01, 0x00, 0x11]);
+      socket.add(<int>[usbSerialRxFrameStart, 0x02, 0x00, 0x33, 0x44]);
+      await socket.flush();
+
+      await Future<void>.delayed(const Duration(milliseconds: 20));
+
+      expect(receivedFrames, hasLength(1));
+      expect(receivedFrames.single, orderedEquals(<int>[0x33, 0x44]));
+    } finally {
+      await service.disconnect();
+      await frameSub.cancel();
+      await serverSub.cancel();
+      await server.close();
+    }
+  });
+
+  test(
+    'disconnect during in-flight connect keeps transport disconnected',
+    () async {
+      final server = await ServerSocket.bind(InternetAddress.loopbackIPv4, 0);
+      final service = TcpTransportService();
+      final host = InternetAddress.loopbackIPv4.address;
+
+      try {
+        await IOOverrides.runWithIOOverrides(() async {
+          final connectFuture = service.connect(host: host, port: server.port);
+
+          await Future<void>.delayed(const Duration(milliseconds: 10));
+          await service.disconnect();
+          await connectFuture;
+
+          expect(service.isConnected, isFalse);
+          expect(service.status, TcpTransportStatus.disconnected);
+          expect(service.activeEndpoint, isNull);
+        }, _DelayedConnectOverrides(const Duration(milliseconds: 120)));
+      } finally {
+        await service.disconnect();
+        await server.close();
+      }
+    },
+  );
+}