feat(alarma-sonando): restyle ringing screen, drop live countdown label

Replace the glass-card container with a full-bleed blurred-art
background, giant heroTime display, 3 fixed snooze tiles (3/5/10 min,
one highlighted), and a full-width stop pill. The status label now
also renders a static "Subiendo volumen" line - no seconds counter -
when the alarm has a configured fade-in, per resolution 4: the
native-to-Flutter progress channel a live counter would need is
deliberately absent from this architecture.

The dismiss guard and force-stop retry banner are untouched: the
banner is byte-identical to its pre-restyle form, only repositioned,
and the guard test's own diff against main stays empty.

size:exception: 530 changed lines (440+/90-) against the 200-300
forecast - lib/ alone is 302 lines, at the edge of the band; the two
touched test files account for the rest. Not split further: this is
one cohesive restyle to the single screen in this branch where an
inconsistent intermediate state is least acceptable.

test/pantallas/pantalla_alarma_sonando_scaffold_test.dart

@@ -11,6 +11,8 @@ import 'package:pluriwave/modelos/emisora.dart';
 import 'package:pluriwave/pantallas/pantalla_alarma_sonando.dart';
 import 'package:pluriwave/servicios/servicio_alarmas.dart';
 import 'package:pluriwave/servicios/servicio_audio.dart';
+import 'package:pluriwave/tema/pluriwave_theme.dart';
+import 'package:pluriwave/widgets/pluri_glass_surface.dart';
 import 'package:pluriwave/widgets/pluri_wave_scaffold.dart';
 import 'package:provider/provider.dart';
 import 'package:shared_preferences/shared_preferences.dart';
@@ -89,9 +91,7 @@ Future<void> _montarPantalla(
     navigator.push(
       MaterialPageRoute<void>(
         builder:
-            (_) => PantallaAlarmaSonando(
-              alarma: estadoAlarmas.alarmas.single,
-            ),
+            (_) => PantallaAlarmaSonando(alarma: estadoAlarmas.alarmas.single),
         fullscreenDialog: true,
       ),
     ),
@@ -143,4 +143,38 @@ void main() {
       expect(find.text(l10n.stopAlarmAction), findsOneWidget);
     },
   );
+
+  group('WU11 — restyle a pantalla completa', () {
+    testWidgets(
+      'el tiempo gigante usa PluriWaveTypography.heroTime envuelto en '
+      'FittedBox(scaleDown)',
+      (tester) async {
+        await _montarPantalla(tester);
+
+        final heroFinder = find.byKey(const ValueKey('ringing-hero-time'));
+        expect(heroFinder, findsOneWidget);
+        final texto = tester.widget<Text>(heroFinder);
+        final contexto = tester.element(heroFinder);
+        expect(texto.style, contexto.pluriType.heroTime);
+        expect(
+          find.ancestor(of: heroFinder, matching: find.byType(FittedBox)),
+          findsOneWidget,
+        );
+      },
+    );
+
+    testWidgets(
+      'el fondo es arte difuminado a pantalla completa; el contenedor '
+      'glass-card anterior desaparece',
+      (tester) async {
+        await _montarPantalla(tester);
+
+        expect(
+          find.byKey(const ValueKey('ringing-background-art')),
+          findsOneWidget,
+        );
+        expect(find.byType(PluriGlassSurface), findsNothing);
+      },
+    );
+  });
 }