fix(alarmas): restyle the editor sheet as the prototype draws it

Audit 8.1-8.4: opaque bottom-anchored sheet with a grab handle, a framed
time card and 7 circular day buttons.

The date field, fallback-station picker and sound dropdown all stay
reachable -- the prototype omits them, but presentation changes never
remove capability.

test/pantallas/pantalla_alarmas_editor_test.dart

@@ -6,6 +6,7 @@ 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:pluriwave/widgets/editor_hora_inline.dart';
 import 'package:pluriwave/widgets/pluri_push_scaffold.dart';
 import 'package:provider/provider.dart';
 import 'package:shared_preferences/shared_preferences.dart';
@@ -294,6 +295,113 @@ void main() {
     expect(volumen.min, 0.0);
   });
 
+  group('visual fidelity (audit 8.1/8.3/8.4, item 20)', () {
+    testWidgets(
+      '8.1: the sheet is an opaque, bottom-anchored surface (radius on the '
+      'top corners only) with a grab handle',
+      (tester) async {
+        await _abrirEditor(tester);
+
+        final surface = tester.widget<DecoratedBox>(
+          find.byKey(const ValueKey('alarm-editor-sheet-surface')),
+        );
+        final decoracion = surface.decoration as BoxDecoration;
+        expect(
+          decoracion.color,
+          const Color(0xFF0D1B24),
+          reason: 't4 line 373: background:#0D1B24 (opaque, not glass)',
+        );
+        expect(
+          decoracion.borderRadius,
+          const BorderRadius.vertical(top: Radius.circular(30)),
+          reason:
+              't4 line 373: border-radius:30px 30px 0 0 — top corners '
+              'only, unlike a floating dialog',
+        );
+
+        final asa = tester.widget<Container>(
+          find.byKey(const ValueKey('alarm-editor-grab-handle')),
+        );
+        expect(asa.constraints?.maxWidth, 44);
+        expect(asa.constraints?.maxHeight, 4);
+        final asaDecoracion = asa.decoration as BoxDecoration;
+        expect(
+          asaDecoracion.borderRadius,
+          BorderRadius.circular(2),
+          reason: 't4 line 374: width:44px;height:4px;border-radius:2px',
+        );
+      },
+    );
+
+    testWidgets('8.3: the hour editor sits inside a framed card', (
+      tester,
+    ) async {
+      await _abrirEditor(tester);
+
+      final tarjeta = tester.widget<DecoratedBox>(
+        find.ancestor(
+          of: find.byType(EditorHoraInline),
+          matching: find.byKey(const ValueKey('alarm-editor-hour-card')),
+        ),
+      );
+      final decoracion = tarjeta.decoration as BoxDecoration;
+      expect(
+        decoracion.borderRadius,
+        BorderRadius.circular(22),
+        reason: 't4 line 378: border-radius:22px',
+      );
+      expect(
+        decoracion.color,
+        const Color(0xFF102532),
+        reason: 't4 line 378: background:#102532 (== listSurface token)',
+      );
+    });
+
+    testWidgets(
+      '8.4: the weekday selector is exactly 7 circular buttons, not chips',
+      (tester) async {
+        await _abrirEditor(tester);
+
+        final fila = find.byKey(const ValueKey('alarm-weekday-circles'));
+        expect(fila, findsOneWidget);
+        expect(
+          find.descendant(of: fila, matching: find.byType(FilterChip)),
+          findsNothing,
+          reason: 't4 lines 383-390: 7 circles, not FilterChips',
+        );
+        final circulos = find.descendant(
+          of: fila,
+          matching: find.byWidgetPredicate(
+            (w) => w is Material && w.shape is CircleBorder,
+          ),
+        );
+        expect(circulos, findsNWidgets(7));
+      },
+    );
+
+    testWidgets(
+      'capacity guard: the date field, the fallback-station picker and the '
+      'sound dropdown all stay reachable behind Advanced',
+      (tester) async {
+        await _abrirEditor(tester);
+
+        await tester.ensureVisible(find.text(l10n.alarmAdvancedSectionTitle));
+        await tester.tap(find.text(l10n.alarmAdvancedSectionTitle));
+        await tester.pumpAndSettle();
+
+        expect(find.text(l10n.dateField), findsOneWidget);
+        expect(
+          find.byKey(const ValueKey('alarm-fallback-station-field')),
+          findsOneWidget,
+        );
+        expect(
+          find.byType(DropdownButtonFormField<SonidoInternoAlarma>),
+          findsOneWidget,
+        );
+      },
+    );
+  });
+
   group('WU8 — tarjeta de alarma simplificada', () {
     testWidgets(
       'tocar la tarjeta abre el editor precargado con los datos de esa '