feat(bienvenida): add monetization-free welcome screen

Build the first-run welcome surface from mockup screen 14, stripped of
its entire monetization block: no PRO pill, no "14 dias PRO gratis"
trial line, no pricing card, no secondary "free version" link. Ships
only logo, headline, body copy, exactly 3 feature bullets, and the
single "Empezar a escuchar" CTA, as a full-screen route (not a modal).

Spanish copy is re-cast from the mockup's "tu" form to the app's
established voseo register (matching ~750 existing app_es.arb lines),
using "auto" instead of "coche" per the one existing precedent. The 3
bullet icons reuse existing tokens (electricMagenta/liveGreen/
warmCoral) that already match the mockup's own hex values for them.

CTA switches to the Escuchar tab and pops the route. Wiring this
screen into the real first-launch flow (main.dart/app.dart) is left
for a follow-up unit, same shape as WU15/WU15b - this WU only covers
the isolated, tested screen per its own task list and verify command.

WU17.

test/pantallas/pantalla_bienvenida_test.dart

@@ -0,0 +1,144 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:pluriwave/estado/estado_navegacion.dart';
+import 'package:pluriwave/l10n/gen/app_localizations.dart';
+import 'package:pluriwave/pantallas/pantalla_bienvenida.dart';
+import 'package:provider/provider.dart';
+
+/// WU17: `onboarding-welcome` spec — full-screen route (not a modal),
+/// content only (logo/headline/body/3 bullets/1 CTA), binding
+/// no-monetization guard, and CTA dismisses to Escuchar with the route
+/// popped.
+Widget _app({required EstadoNavegacionRaiz navegacion}) {
+  return ChangeNotifierProvider<EstadoNavegacionRaiz>.value(
+    value: navegacion,
+    child: const MaterialApp(
+      locale: Locale('es'),
+      localizationsDelegates: AppLocalizations.localizationsDelegates,
+      supportedLocales: AppLocalizations.supportedLocales,
+      home: PantallaBienvenida(),
+    ),
+  );
+}
+
+void main() {
+  testWidgets(
+    'renders as a full-screen route with a logo, headline, body copy, '
+    'exactly 3 feature bullets, and exactly one primary CTA',
+    (tester) async {
+      final navegacion = EstadoNavegacionRaiz();
+      addTearDown(navegacion.dispose);
+
+      await tester.pumpWidget(_app(navegacion: navegacion));
+      await tester.pumpAndSettle();
+
+      // A full-screen route, never a modal dialog.
+      expect(find.byType(Dialog), findsNothing);
+      expect(find.byType(AlertDialog), findsNothing);
+      expect(find.byType(Scaffold), findsOneWidget);
+
+      expect(find.byType(Image), findsOneWidget, reason: 'the logo mark');
+      expect(find.text('Tu mundo, en directo'), findsOneWidget);
+      expect(
+        find.textContaining('53.412 emisoras de 238 países'),
+        findsOneWidget,
+      );
+      expect(
+        find.byType(FilaCaracteristicaBienvenida),
+        findsNWidgets(3),
+        reason: 'exactly 3 feature bullets',
+      );
+      expect(
+        find.byType(FilledButton),
+        findsOneWidget,
+        reason: 'exactly 1 primary CTA',
+      );
+      expect(find.text('Empezar a escuchar'), findsOneWidget);
+    },
+  );
+
+  testWidgets('rendered content contains no monetization strings', (
+    tester,
+  ) async {
+    final navegacion = EstadoNavegacionRaiz();
+    addTearDown(navegacion.dispose);
+
+    await tester.pumpWidget(_app(navegacion: navegacion));
+    await tester.pumpAndSettle();
+
+    final textoCompleto = tester
+        .widgetList<Text>(find.byType(Text))
+        .map((widget) => widget.data ?? '')
+        .join('\n');
+
+    expect(textoCompleto.contains('PRO'), isFalse);
+    expect(textoCompleto.contains('€'), isFalse);
+    expect(textoCompleto.contains(r'$'), isFalse);
+    expect(
+      RegExp(r'\d+\s*d[ií]as?\b', caseSensitive: false).hasMatch(
+        textoCompleto,
+      ),
+      isFalse,
+      reason: 'no day-count trial phrase (e.g. "14 días")',
+    );
+    expect(
+      find.textContaining('gratuita', findRichText: true),
+      findsNothing,
+      reason: 'no secondary "free version" link',
+    );
+    expect(
+      find.textContaining('gratis', findRichText: true),
+      findsNothing,
+      reason: 'no secondary "free version" link',
+    );
+    // Only one tappable action on the whole screen: the primary CTA.
+    expect(find.byType(TextButton), findsNothing);
+    expect(find.byType(FilledButton), findsOneWidget);
+  });
+
+  testWidgets(
+    'tapping the primary CTA switches to Escuchar and pops the welcome route',
+    (tester) async {
+      // Start on a DIFFERENT tab so a pass actually proves irA() ran,
+      // rather than coasting on EstadoNavegacionRaiz's own escuchar default.
+      final navegacion = EstadoNavegacionRaiz()
+        ..irA(RaizPluriWave.ajustes);
+      addTearDown(navegacion.dispose);
+      final navigatorKey = GlobalKey<NavigatorState>();
+
+      await tester.pumpWidget(
+        ChangeNotifierProvider<EstadoNavegacionRaiz>.value(
+          value: navegacion,
+          child: MaterialApp(
+            navigatorKey: navigatorKey,
+            locale: const Locale('es'),
+            localizationsDelegates: AppLocalizations.localizationsDelegates,
+            supportedLocales: AppLocalizations.supportedLocales,
+            home: const Scaffold(body: Center(child: Text('home stand-in'))),
+          ),
+        ),
+      );
+
+      unawaited(
+        navigatorKey.currentState!.push(
+          MaterialPageRoute<void>(builder: (_) => const PantallaBienvenida()),
+        ),
+      );
+      await tester.pumpAndSettle();
+      expect(find.byType(PantallaBienvenida), findsOneWidget);
+
+      await tester.tap(find.text('Empezar a escuchar'));
+      await tester.pumpAndSettle();
+
+      expect(navegacion.actual, RaizPluriWave.escuchar);
+      expect(
+        find.byType(PantallaBienvenida),
+        findsNothing,
+        reason: 'the welcome route was removed from the back stack',
+      );
+      expect(find.text('home stand-in'), findsOneWidget);
+    },
+  );
+}