fix: report a user-requested stop as stopped rather than failed

Stopping a test shuts down the control socket, so iperf_run_client() returns
-1 with "unable to send control message ... Broken pipe". That is the
expected consequence of the stop, not a fault, but the bridge read the
negative return as a failure — so pressing STOP left the UI showing
"Error (exit 1)" above a broken-pipe message.

The bridge now consults its own g_stop flag before classifying the outcome,
and the distinction travels up as Iperf3Result.stopped so the status line can
say "Stopped". A stop is reported with exit code 0: the run ended the way the
user asked it to.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

test/ui/features/test_run/test_run_view_model_test.dart

@@ -120,6 +120,31 @@ void main() {
       await run;
     });
 
+    test('wasStopped reflects a user-requested stop', () async {
+      final mock = _MockIperf3Service(
+        onRun: (_) async => const Iperf3Result(
+          rawOutput: 'stopped early',
+          exitCode: 0,
+          stopped: true,
+        ),
+      );
+      final vm = TestRunViewModel(iperf3Service: mock);
+      await vm.runTest(const TestConfiguration(server: '192.168.1.1'));
+      // A user stop is a normal outcome: completed, not error.
+      expect(vm.state, equals(TestRunState.completed));
+      expect(vm.wasStopped, isTrue);
+    });
+
+    test('wasStopped is false for a run that finished on its own', () async {
+      final mock = _MockIperf3Service(
+        onRun: (_) async =>
+            const Iperf3Result(rawOutput: 'done', exitCode: 0),
+      );
+      final vm = TestRunViewModel(iperf3Service: mock);
+      await vm.runTest(const TestConfiguration(server: '192.168.1.1'));
+      expect(vm.wasStopped, isFalse);
+    });
+
     test('a second runTest while running is ignored', () async {
       final mock = _MockIperf3Service();
       final gate = Completer<Iperf3Result>();