feat(i18n): add localization foundation

lib/pantallas/pantalla_ajustes.dart

@@ -9,7 +9,9 @@ import 'package:provider/provider.dart';
 import 'package:share_plus/share_plus.dart' show Share, XFile;
 import 'package:uuid/uuid.dart';
 
+import '../estado/estado_idioma.dart';
 import '../estado/estado_radio.dart';
+import '../l10n/gen/app_localizations.dart';
 import '../modelos/emisora.dart';
 import '../widgets/ecualizador_widget.dart';
 import '../widgets/pluri_glass_surface.dart';
@@ -22,20 +24,21 @@ class PantallaAjustes extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final l10n = AppLocalizations.of(context);
+
     return ListView(
       padding: PluriLayout.pageListPadding,
-      children: const [
+      children: [
         PluriScreenHeader(
-          title: 'Ajustes',
-          subtitle:
-              'Control fino de sonido, copias de seguridad y emisoras personalizadas.',
+          title: l10n.settingsTitle,
+          subtitle: l10n.settingsSubtitle,
           glyph: PluriIconGlyph.settings,
-          trailing: PluriStatusPill(
+          trailing: const PluriStatusPill(
             icon: Icons.security_rounded,
             label: 'Seguro',
           ),
         ),
-        Padding(
+        const Padding(
           padding: PluriLayout.pageContentPadding,
           child: _AjustesContent(),
         ),
@@ -57,6 +60,8 @@ class _AjustesContent extends StatelessWidget {
         SizedBox(height: 12),
         _SeccionTimerSueno(),
         SizedBox(height: 12),
+        _SeccionIdioma(),
+        SizedBox(height: 12),
         _SeccionEmisoraPreferida(),
         SizedBox(height: 12),
         _SeccionEmisoras(),
@@ -165,6 +170,8 @@ class _SeccionTimerSueno extends StatelessWidget {
   const _SeccionTimerSueno();
 
   Future<void> _anadirPreset(BuildContext context) async {
+    final l10n = AppLocalizations.of(context);
+
     final duracion = await showModalBottomSheet<Duration>(
       context: context,
       isScrollControlled: true,
@@ -177,7 +184,7 @@ class _SeccionTimerSueno extends StatelessWidget {
     ScaffoldMessenger.of(context).showSnackBar(
       SnackBar(
         content: Text(
-          'Acceso rápido añadido: ${_formatearDuracionTimer(duracion)}',
+          '${l10n.saveQuickAccessButton}: ${_formatearDuracionTimer(duracion)}',
         ),
       ),
     );
@@ -185,6 +192,8 @@ class _SeccionTimerSueno extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final l10n = AppLocalizations.of(context);
+
     final estado = context.watch<EstadoRadio>();
     final presets = estado.timerSuenoPresetsSegundos;
     return PluriGlassSurface(
@@ -196,20 +205,20 @@ class _SeccionTimerSueno extends StatelessWidget {
               const Icon(Icons.bedtime_rounded),
               const SizedBox(width: 12),
               Text(
-                'Timer de sueño',
+                l10n.timerSectionTitle,
                 style: Theme.of(context).textTheme.titleMedium,
               ),
               const Spacer(),
               TextButton.icon(
                 icon: const Icon(Icons.add_rounded),
-                label: const Text('Añadir'),
+                label: Text(l10n.timerSectionAdd),
                 onPressed: () => _anadirPreset(context),
               ),
             ],
           ),
           const SizedBox(height: 8),
           Text(
-            'Personalizá los accesos rápidos que aparecen al apagar la radio automáticamente.',
+            l10n.timerSectionDescription,
             style: Theme.of(context).textTheme.bodySmall,
           ),
           const SizedBox(height: 12),
@@ -236,7 +245,7 @@ class _SeccionTimerSueno extends StatelessWidget {
             alignment: Alignment.centerLeft,
             child: TextButton.icon(
               icon: const Icon(Icons.restore_rounded),
-              label: const Text('Restaurar tiempos recomendados'),
+              label: Text(l10n.timerSectionRestoreRecommended),
               onPressed:
                   () => context.read<EstadoRadio>().restaurarTimerSuenoPresets(),
             ),
@@ -247,6 +256,95 @@ class _SeccionTimerSueno extends StatelessWidget {
   }
 }
 
+class _SeccionIdioma extends StatelessWidget {
+  const _SeccionIdioma();
+
+  static const _codigoSistema = 'system';
+  static const _codigoEspanol = 'es';
+  static const _codigoIngles = 'en';
+
+  @override
+  Widget build(BuildContext context) {
+    final l10n = AppLocalizations.of(context);
+    final estadoIdioma = context.watch<EstadoIdioma>();
+    final locale = estadoIdioma.localeSeleccionado;
+    final valorActual = switch (locale?.languageCode) {
+      _codigoEspanol => _codigoEspanol,
+      _codigoIngles => _codigoIngles,
+      _ => _codigoSistema,
+    };
+
+    return PluriGlassSurface(
+      child: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          Row(
+            children: [
+              const Icon(Icons.language_rounded),
+              const SizedBox(width: 12),
+              Text(
+                l10n.languageSectionTitle,
+                style: Theme.of(context).textTheme.titleMedium,
+              ),
+            ],
+          ),
+          const SizedBox(height: 8),
+          Text(
+            l10n.languageSectionDescription,
+            style: Theme.of(context).textTheme.bodySmall,
+          ),
+          const SizedBox(height: 12),
+          DropdownButtonFormField<String>(
+            initialValue: valorActual,
+            decoration: InputDecoration(
+              labelText: l10n.languageSectionTitle,
+              border: const OutlineInputBorder(),
+            ),
+            items: [
+              DropdownMenuItem(
+                value: _codigoSistema,
+                child: Text(l10n.languageSystemDefault),
+              ),
+              DropdownMenuItem(
+                value: _codigoEspanol,
+                child: Text(l10n.languageSpanish),
+              ),
+              DropdownMenuItem(
+                value: _codigoIngles,
+                child: Text(l10n.languageEnglish),
+              ),
+            ],
+            onChanged: (codigo) async {
+              if (codigo == null) return;
+              if (codigo == _codigoSistema) {
+                await context.read<EstadoIdioma>().seleccionarSistema();
+                if (!context.mounted) return;
+                ScaffoldMessenger.of(context).showSnackBar(
+                  SnackBar(content: Text(l10n.languageUpdatedSystem)),
+                );
+                return;
+              }
+
+              final locale = Locale(codigo);
+              await context.read<EstadoIdioma>().seleccionarLocale(locale);
+              if (!context.mounted) return;
+
+              final nombre = switch (codigo) {
+                _codigoEspanol => l10n.languageSpanish,
+                _codigoIngles => l10n.languageEnglish,
+                _ => l10n.languageSystemDefault,
+              };
+              ScaffoldMessenger.of(context).showSnackBar(
+                SnackBar(content: Text(l10n.languageUpdated(nombre))),
+              );
+            },
+          ),
+        ],
+      ),
+    );
+  }
+}
+
 class _FormularioDuracionTimer extends StatefulWidget {
   const _FormularioDuracionTimer();
 
@@ -270,6 +368,8 @@ class _FormularioDuracionTimerState extends State<_FormularioDuracionTimer> {
   int _leer(TextEditingController ctrl) => int.tryParse(ctrl.text.trim()) ?? 0;
 
   void _guardar() {
+    final l10n = AppLocalizations.of(context);
+
     final duracion = Duration(
       hours: _leer(_horasCtrl),
       minutes: _leer(_minutosCtrl),
@@ -277,7 +377,7 @@ class _FormularioDuracionTimerState extends State<_FormularioDuracionTimer> {
     );
     if (duracion <= Duration.zero) {
       ScaffoldMessenger.of(context).showSnackBar(
-        const SnackBar(content: Text('Elegí una duración mayor que cero.')),
+        SnackBar(content: Text(l10n.durationGreaterThanZero)),
       );
       return;
     }
@@ -286,6 +386,8 @@ class _FormularioDuracionTimerState extends State<_FormularioDuracionTimer> {
 
   @override
   Widget build(BuildContext context) {
+    final l10n = AppLocalizations.of(context);
+
     final bottom = MediaQuery.viewInsetsOf(context).bottom;
     return SafeArea(
       child: Padding(
@@ -295,23 +397,23 @@ class _FormularioDuracionTimerState extends State<_FormularioDuracionTimer> {
           crossAxisAlignment: CrossAxisAlignment.stretch,
           children: [
             Text(
-              'Nuevo acceso rápido',
+              l10n.newQuickAccessTitle,
               style: Theme.of(context).textTheme.titleLarge,
             ),
             const SizedBox(height: 12),
             Row(
               children: [
-                Expanded(child: _campo(_horasCtrl, 'Horas')),
+                Expanded(child: _campo(_horasCtrl, l10n.hoursLabel)),
                 const SizedBox(width: 8),
-                Expanded(child: _campo(_minutosCtrl, 'Minutos')),
+                Expanded(child: _campo(_minutosCtrl, l10n.minutesLabel)),
                 const SizedBox(width: 8),
-                Expanded(child: _campo(_segundosCtrl, 'Segundos')),
+                Expanded(child: _campo(_segundosCtrl, l10n.secondsLabel)),
               ],
             ),
             const SizedBox(height: 16),
             FilledButton.icon(
               icon: const Icon(Icons.save_rounded),
-              label: const Text('Guardar acceso rápido'),
+              label: Text(l10n.saveQuickAccessButton),
               onPressed: _guardar,
             ),
           ],