fix(bienvenida): wire the welcome screen into the first-launch flow

test/pantallas/pantalla_bienvenida_primer_lanzamiento_test.dart

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+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:pluriwave/l10n/gen/app_localizations.dart';
+import 'package:pluriwave/pantallas/pantalla_bienvenida.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+/// WU17b: `PantallaBienvenida.mostrarSiProcede` wires the welcome screen
+/// into the genuine first-launch flow. WU17 built and tested the screen
+/// fully in isolation, but nothing in `lib/app.dart` or `lib/main.dart`
+/// ever referenced it — it was unreachable. These tests pin the actual
+/// gap: the screen must show on a genuine first launch and never again
+/// once `ServicioBienvenida` has recorded it as seen.
+Widget _appConDisparador(GlobalKey<NavigatorState> navigatorKey) {
+  return MaterialApp(
+    navigatorKey: navigatorKey,
+    locale: const Locale('es'),
+    localizationsDelegates: AppLocalizations.localizationsDelegates,
+    supportedLocales: AppLocalizations.supportedLocales,
+    home: Builder(
+      builder:
+          (context) => Scaffold(
+            body: Center(
+              child: ElevatedButton(
+                onPressed: () => PantallaBienvenida.mostrarSiProcede(context),
+                child: const Text('disparar'),
+              ),
+            ),
+          ),
+    ),
+  );
+}
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  testWidgets(
+    'first launch (no seen flag persisted) shows the welcome screen',
+    (tester) async {
+      SharedPreferences.setMockInitialValues({});
+      final navigatorKey = GlobalKey<NavigatorState>();
+
+      await tester.pumpWidget(_appConDisparador(navigatorKey));
+      await tester.tap(find.text('disparar'));
+      await tester.pumpAndSettle();
+
+      expect(find.byType(PantallaBienvenida), findsOneWidget);
+    },
+  );
+
+  testWidgets(
+    'second launch (seen flag already persisted) does not show it again',
+    (tester) async {
+      SharedPreferences.setMockInitialValues({
+        'pluri_bienvenida_vista_v1': true,
+      });
+      final navigatorKey = GlobalKey<NavigatorState>();
+
+      await tester.pumpWidget(_appConDisparador(navigatorKey));
+      await tester.tap(find.text('disparar'));
+      await tester.pumpAndSettle();
+
+      expect(find.byType(PantallaBienvenida), findsNothing);
+    },
+  );
+
+  testWidgets('showing it once persists the flag so a later check in the same '
+      'session skips it', (tester) async {
+    SharedPreferences.setMockInitialValues({});
+    final navigatorKey = GlobalKey<NavigatorState>();
+
+    await tester.pumpWidget(_appConDisparador(navigatorKey));
+    await tester.tap(find.text('disparar'));
+    await tester.pumpAndSettle();
+    expect(find.byType(PantallaBienvenida), findsOneWidget);
+
+    // Dismiss it the same way the CTA does (a plain pop), simulating the
+    // welcome screen being resolved before the next check ever happens.
+    navigatorKey.currentState!.pop();
+    await tester.pumpAndSettle();
+
+    await tester.tap(find.text('disparar'));
+    await tester.pumpAndSettle();
+    expect(find.byType(PantallaBienvenida), findsNothing);
+  });
+}

test/servicios/servicio_bienvenida_test.dart

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+import 'package:flutter_test/flutter_test.dart';
+import 'package:pluriwave/servicios/servicio_bienvenida.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+/// WU17b: `ServicioBienvenida` decides whether the first-run welcome
+/// screen (`PantallaBienvenida`) is still due — same injectable-prefs,
+/// versioned-key convention as `ServicioContenidoApp` (S3-R4), but a plain
+/// boolean flag since this welcome is a one-time, not per-version, surface.
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  group('ServicioBienvenida', () {
+    test(
+      'debeMostrarBienvenida is true before it has ever been marked seen',
+      () async {
+        SharedPreferences.setMockInitialValues({});
+        final servicio = ServicioBienvenida();
+
+        expect(await servicio.debeMostrarBienvenida(), isTrue);
+      },
+    );
+
+    test(
+      'debeMostrarBienvenida is false after marcarBienvenidaVista',
+      () async {
+        SharedPreferences.setMockInitialValues({});
+        final servicio = ServicioBienvenida();
+
+        await servicio.marcarBienvenidaVista();
+
+        expect(await servicio.debeMostrarBienvenida(), isFalse);
+      },
+    );
+
+    test('respects a seen flag already persisted by a prior launch', () async {
+      SharedPreferences.setMockInitialValues({
+        'pluri_bienvenida_vista_v1': true,
+      });
+      final servicio = ServicioBienvenida();
+
+      expect(await servicio.debeMostrarBienvenida(), isFalse);
+    });
+  });
+}