feat(tutorial): add 9-screen help/tutorial carousel

Add PantallaTutorialAyuda, a PageView-based carousel covering saved
stations/groups, per-station equalizer, recording, adaptive alarms,
Android Auto favorites, auto-reconnect, snooze duration, custom
stations, and a closing summary with a "watch it again" reminder.

ServicioTutorialAyuda persists a one-time seen flag so the carousel
shows once via mostrarSiProcede, independent of entry point; the
final page's CTA label depends on the primerArranque constructor
parameter ("Empezar a escuchar" vs "Cerrar").

Translate the new copy into all 13 supported locales and update
helpSubtitle to describe the new entry point.

test/widgets/pluri_root_header_test.dart

@@ -12,12 +12,23 @@ import 'package:pluriwave/widgets/pluri_root_header.dart';
 /// sleep-timer action that used to live on `app.dart`'s single global
 /// `AppBar` stays reachable from every tab.
 void main() {
-  Widget host(Widget child) {
+  // [topInset] simulates `MediaQuery.paddingOf(context).top` (status bar /
+  // camera cutout) — the same technique already used by
+  // `pantalla_alarma_sonando_scaffold_test.dart`'s `MediaQuery` override via
+  // `MaterialApp.builder`.
+  Widget host(Widget child, {double topInset = 0}) {
     return MaterialApp(
       theme: PluriWaveTheme.dark(),
       locale: const Locale('en'),
       localizationsDelegates: AppLocalizations.localizationsDelegates,
       supportedLocales: AppLocalizations.supportedLocales,
+      builder:
+          (context, app) => MediaQuery(
+            data: MediaQuery.of(
+              context,
+            ).copyWith(padding: EdgeInsets.only(top: topInset)),
+            child: app!,
+          ),
       home: Scaffold(body: child),
     );
   }
@@ -42,7 +53,13 @@ void main() {
       host(PluriRootHeader(title: 'Settings', onSleepTimer: () {})),
     );
 
-    final padding = tester.widget<Padding>(find.byType(Padding).first);
+    // Keyed lookup (not `find.byType(Padding).first`): the top-inset fix
+    // wraps this content padding in an outer `Padding(top: topInset)`, so
+    // `.first` would no longer reliably resolve to the content row's own
+    // padding.
+    final padding = tester.widget<Padding>(
+      find.byKey(const ValueKey('pluri-root-header-content')),
+    );
     final insets = padding.padding as EdgeInsets;
     expect(insets.left, PluriLayout.titleHorizontal);
     expect(insets.right, PluriLayout.rowHorizontal);
@@ -97,4 +114,92 @@ void main() {
       reason: 'actions render before (to the left of) the bedtime button',
     );
   });
+
+  group('fix top-inset: total height and content position track '
+      'MediaQuery.paddingOf(context).top, instead of always sitting flush '
+      'at y=0 under the status bar', () {
+    // Vertical text centering inside the 56px content row means the
+    // title's own top-left never sits exactly AT the header's top-left
+    // (even at topInset=0) — so these tests compare each inset's title
+    // position against the topInset=0 BASELINE, isolating exactly the
+    // inset's own contribution instead of asserting a brittle absolute
+    // offset.
+    Future<double> tituloTopPara(WidgetTester tester, double topInset) async {
+      await tester.pumpWidget(
+        host(
+          PluriRootHeader(title: 'Settings', onSleepTimer: () {}),
+          topInset: topInset,
+        ),
+      );
+      return tester.getTopLeft(find.text('Settings')).dy;
+    }
+
+    testWidgets(
+      'topInset=0 (e.g. desktop/no cutout): total height stays the plain '
+      '56px content height',
+      (tester) async {
+        await tester.pumpWidget(
+          host(PluriRootHeader(title: 'Settings', onSleepTimer: () {})),
+        );
+
+        expect(tester.getSize(find.byType(PluriRootHeader)).height, 56);
+      },
+    );
+
+    testWidgets(
+      'topInset=24 (typical status bar): total height becomes 56+24=80, '
+      'and the title shifts down by exactly the inset relative to the '
+      'topInset=0 baseline',
+      (tester) async {
+        final base = await tituloTopPara(tester, 0);
+        final conInset = await tituloTopPara(tester, 24);
+
+        expect(tester.getSize(find.byType(PluriRootHeader)).height, 80);
+        expect(conInset - base, 24);
+      },
+    );
+
+    testWidgets(
+      'topInset=44 (taller status bar): total height becomes 56+44=100, '
+      'and the title still shifts down by exactly the inset — never '
+      'clipped',
+      (tester) async {
+        final base = await tituloTopPara(tester, 0);
+        final conInset = await tituloTopPara(tester, 44);
+
+        expect(tester.getSize(find.byType(PluriRootHeader)).height, 100);
+        expect(conInset - base, 44);
+      },
+    );
+
+    testWidgets(
+      'topInset=60 (notch/camera-cutout simulation): total height becomes '
+      '56+60=116, and the title still fully clears the inset — never '
+      'overlapping it',
+      (tester) async {
+        final base = await tituloTopPara(tester, 0);
+        final conInset = await tituloTopPara(tester, 60);
+
+        expect(tester.getSize(find.byType(PluriRootHeader)).height, 116);
+        expect(conInset - base, 60);
+      },
+    );
+
+    testWidgets(
+      'PluriRootHeader.height stays the CONTENT height (56) regardless of '
+      'inset — callers doing total-height math must separately add '
+      'MediaQuery.paddingOf(context).top',
+      (tester) async {
+        await tester.pumpWidget(
+          host(
+            PluriRootHeader(title: 'Settings', onSleepTimer: () {}),
+            topInset: 44,
+          ),
+        );
+
+        expect(PluriRootHeader.height, 56);
+        expect(tester.getSize(find.byType(PluriRootHeader)).height, 100);
+      },
+    );
+  });
 }