fix(alarmas): tighten the gap between stacked alarm cards to 10px

Tier 4 visual fidelity, audit 7.5 (t4 line 334): the prototype stacks
alarm cards with a 10px gap; the build used 12. Each gap is now keyed
per alarm id so a guard test can pin the exact value between two known
cards.

lib/pantallas/pantalla_alarmas.dart

@@ -63,7 +63,14 @@ class PantallaAlarmas extends StatelessWidget {
                 else
                   for (final alarma in estado.alarmas) ...[
                     _TarjetaAlarma(alarma: alarma),
-                    const SizedBox(height: 12),
+                    // 7.5 (Tier 4 visual fidelity): the prototype's gap
+                    // between stacked alarm cards is 10px (t4 line 334),
+                    // not 12. Keyed per alarm id so the guard test can
+                    // target the exact gap between two known cards.
+                    SizedBox(
+                      height: 10,
+                      key: ValueKey('alarm-card-gap-${alarma.id}'),
+                    ),
                   ],
                 _PanelVacaciones(estado: estado),
                 const SizedBox(height: 12),

test/pantallas/pantalla_alarmas_card_gap_test.dart

@@ -0,0 +1,90 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:pluriwave/estado/estado_alarmas.dart';
+import 'package:pluriwave/estado/estado_radio.dart';
+import 'package:pluriwave/l10n/gen/app_localizations.dart';
+import 'package:pluriwave/modelos/alarma_musical.dart';
+import 'package:pluriwave/pantallas/pantalla_alarmas.dart';
+import 'package:pluriwave/servicios/servicio_alarmas.dart';
+import 'package:provider/provider.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+import '../helpers/fakes.dart';
+import '../helpers/fakes_alarmas.dart';
+
+/// Audit 7.5 (Tier 4 visual fidelity): the prototype's gap between stacked
+/// alarm cards is 10px (t4 line 334, `gap:10` on the alarms column), not the
+/// build's previous 12px.
+void main() {
+  setUp(() {
+    SharedPreferences.setMockInitialValues({});
+  });
+
+  testWidgets('spaces stacked alarm cards 10px apart, not 12', (tester) async {
+    tester.view.physicalSize = const Size(1440, 3200);
+    tester.view.devicePixelRatio = 1.0;
+    addTearDown(tester.view.resetPhysicalSize);
+    addTearDown(tester.view.resetDevicePixelRatio);
+
+    final radio = EstadoRadio(
+      audio: FakeServicioAudio(),
+      favoritos: FakeServicioFavoritos(),
+      radio: FakeServicioRadio(),
+      servicioEcualizador: FakeServicioEcualizador(),
+      servicioGrabacion: FakeServicioGrabacionRadioInactiva(),
+      iniciarAutomaticamente: false,
+    );
+    addTearDown(radio.dispose);
+
+    final android = FakePuertoAlarmasAndroid();
+    final estadoAlarmas = EstadoAlarmas(
+      servicio: ServicioAlarmas(reloj: () => DateTime(2026, 6, 11, 6, 0)),
+      android: android,
+      iniciarAutomaticamente: false,
+    );
+    addTearDown(estadoAlarmas.dispose);
+    addTearDown(android.dispose);
+    await estadoAlarmas.guardarAlarma(
+      const AlarmaMusical(
+        id: 'card-gap-a',
+        nombre: 'Primera',
+        hora: 7,
+        minuto: 0,
+        tipoProgramacion: TipoProgramacionAlarma.diaria,
+        diasSemana: [],
+      ),
+    );
+    await estadoAlarmas.guardarAlarma(
+      const AlarmaMusical(
+        id: 'card-gap-b',
+        nombre: 'Segunda',
+        hora: 8,
+        minuto: 0,
+        tipoProgramacion: TipoProgramacionAlarma.diaria,
+        diasSemana: [],
+      ),
+    );
+
+    await tester.pumpWidget(
+      MultiProvider(
+        providers: [
+          ChangeNotifierProvider<EstadoRadio>.value(value: radio),
+          ChangeNotifierProvider<EstadoAlarmas>.value(value: estadoAlarmas),
+        ],
+        child: MaterialApp(
+          locale: const Locale('es'),
+          localizationsDelegates: AppLocalizations.localizationsDelegates,
+          supportedLocales: AppLocalizations.supportedLocales,
+          home: const Scaffold(body: PantallaAlarmas()),
+        ),
+      ),
+    );
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 100));
+
+    final gap = tester.widget<SizedBox>(
+      find.byKey(const ValueKey('alarm-card-gap-card-gap-a')),
+    );
+    expect(gap.height, 10);
+  });
+}