feat(alarmas): surface scheduling failures on the alarm card

Wires EstadoAlarmas.ultimaExcepcionPara into PantallaAlarmas: an
alarm with an outstanding scheduling-failure exception now shows a
calm warning line (distinguishing a pre-notice-only failure from the
alarm itself not being registered) with a tap target into the
reliability diagnostics screen. The warning is its own small tap
target nested inside the existing card InkWell, so tap-to-edit,
swipe-to-delete and the hero "Saltar" chip are untouched.

Adds alarmCardSchedulingFailedMessage/alarmCardPreNoticeFailedMessage
to all 13 ARB locales with real per-language translations (verified
against arb_parity_test and arb_anti_copy_test).

lib/pantallas/pantalla_alarmas.dart

@@ -286,6 +286,20 @@ class _TarjetaAlarma extends StatelessWidget {
       if (pausadaPorVacaciones) l10n.alarmCardVacationPausedBadge,
     ];
 
+    // fix/alarmas-fallos-silenciosos: `ultimaExcepcionPara` existed but was
+    // never read from any screen, so a failed native scheduling attempt (main
+    // alarm, pre-notice, foreground service, or a post-boot reschedule)
+    // rendered exactly like a healthy alarm -- switched on, no visible sign
+    // anything was wrong. `_esValida` only ever treats `tipoSaltoSiguiente`
+    // as a real skip, so any OTHER tipo found here is a reliability failure,
+    // never a deliberate user action.
+    final ultimaExcepcion = estado.ultimaExcepcionPara(alarma.id);
+    final fallo =
+        ultimaExcepcion != null &&
+                ExcepcionAlarma.tiposFallo.contains(ultimaExcepcion.tipo)
+            ? ultimaExcepcion
+            : null;
+
     return Dismissible(
       key: ValueKey('tarjeta-alarma-${alarma.id}'),
       direction: DismissDirection.horizontal,
@@ -417,6 +431,14 @@ class _TarjetaAlarma extends StatelessWidget {
                             ),
                           ),
                         ],
+                        if (fallo != null) ...[
+                          const SizedBox(height: 6),
+                          _AvisoFalloProgramacion(
+                            alarmaId: alarma.id,
+                            esSoloPreaviso:
+                                fallo.tipo == ExcepcionAlarma.tipoFalloPreaviso,
+                          ),
+                        ],
                       ],
                     ),
                   ),
@@ -470,6 +492,82 @@ class _TarjetaAlarma extends StatelessWidget {
   }
 }
 
+/// Per-alarm scheduling-failure notice (fix/alarmas-fallos-silenciosos):
+/// renders INSIDE the card's own content, in its own small tap target --
+/// the surrounding card `InkWell` (tap = edit) and `Dismissible` (swipe =
+/// delete) are untouched; this inner `InkWell` only claims its own region
+/// and pushes the diagnostics screen instead of opening the editor.
+class _AvisoFalloProgramacion extends StatelessWidget {
+  const _AvisoFalloProgramacion({
+    required this.alarmaId,
+    required this.esSoloPreaviso,
+  });
+
+  final String alarmaId;
+
+  /// True when only the pre-notice reminder failed (the alarm itself is
+  /// still scheduled) -- the user's reported symptom explicitly called out
+  /// a missing pre-notice as distinct from the alarm never ringing at all,
+  /// so the message must not conflate the two.
+  final bool esSoloPreaviso;
+
+  @override
+  Widget build(BuildContext context) {
+    final l10n = AppLocalizations.of(context);
+    final color = Theme.of(context).colorScheme.error;
+    return Material(
+      type: MaterialType.transparency,
+      child: InkWell(
+        key: ValueKey('tarjeta-alarma-fallo-$alarmaId'),
+        borderRadius: BorderRadius.circular(8),
+        onTap: () => _abrirDiagnostico(context),
+        child: Padding(
+          padding: const EdgeInsets.symmetric(vertical: 2),
+          child: Row(
+            crossAxisAlignment: CrossAxisAlignment.start,
+            children: [
+              Icon(Icons.warning_amber_rounded, size: 15, color: color),
+              const SizedBox(width: 6),
+              Expanded(
+                child: Column(
+                  crossAxisAlignment: CrossAxisAlignment.start,
+                  mainAxisSize: MainAxisSize.min,
+                  children: [
+                    Text(
+                      esSoloPreaviso
+                          ? l10n.alarmCardPreNoticeFailedMessage
+                          : l10n.alarmCardSchedulingFailedMessage,
+                      style: TextStyle(
+                        fontSize: 11,
+                        fontWeight: FontWeight.w600,
+                        color: color,
+                      ),
+                    ),
+                    const SizedBox(height: 2),
+                    Text(
+                      l10n.androidReliabilityReview,
+                      style: TextStyle(
+                        fontSize: 11,
+                        fontWeight: FontWeight.w800,
+                        color: color,
+                        decoration: TextDecoration.underline,
+                      ),
+                    ),
+                  ],
+                ),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+
+  void _abrirDiagnostico(BuildContext context) {
+    PluriPushScaffold.push(context, (_) => const PantallaDiagnosticoAlarmas());
+  }
+}
+
 /// Swipe-to-delete reveal, shown on both sides so either swipe direction
 /// works regardless of locale text direction.
 class _FondoSwipeEliminarAlarma extends StatelessWidget {