fix(alarmas,auto): guard the last unguarded snooze path, surface car progress

Continuation of 7054a4c: the native anchor guard alone did not fix the
reported ~1444-minute snooze, because Dart runs AFTERWARDS on the
pre-notice path and had no guard at all.

1. Snooze from the pre-notice notification, root cause.

app.dart dispatches AFTER the receiver's postponeNext already ran and
after startActivity, and EstadoAlarmas.posponerProximaDesdePreaviso took
whatever occurrence it was handed on faith, then persisted and
rescheduled from it -- the last snooze path in the codebase with no
occurrence guard. The occurrence itself is not trustworthy either:
app.dart falls back to alarma.proximaEjecucion when the native event
carries none, and that field can already point at tomorrow.

_ocurrenciaSonando is generalized into _ocurrenciaValida with a caller-
supplied forward allowance and an externally-proposed occurrence that
still has to survive the same check. The pre-notice path gets a
ventanaPreaviso (30 min, matching AlarmScheduler.PRE_NOTICE_MILLIS) --
unlike the ringing-screen guard, this occurrence legitimately has not
happened yet, which is exactly why the existing helper could not just be
reused here.

Also heals state already poisoned by the missing guard: a snoozeHasta
parked past a 3-hour ceiling (posponerEjecucion clamps to 120 minutes,
so anything beyond that is corruption, not a long real snooze) is
dropped on recalculation. Without it, an alarm poisoned on a build
before this fix keeps reporting tomorrow after updating, and the user
reasonably concludes nothing changed.

2. Android Auto: no progress bar or time labels on a local track.

updatePosition was never set anywhere in the handler, so it sat at its
Duration.zero default while copyWith refreshed updateTime to now on every
push -- the car was told "position 0, as of right now" on every event, a
bar pinned at the start regardless of what was actually playing. Now set
from _player.position on both the player-state and buffered-position
listeners (the latter ticks ~2/s, which is what keeps the car's bar
smooth between player-state events). Also stream the MediaItem's
duration once the source reports it -- Auto draws no bar at all without
one, and radio streams correctly keep reporting none (live audio has no
length).

3. Android Auto: drop the Ecualizador browsable folder.

Owner decision after driving with it: a browsable six-preset list is
more interaction than a driver wants, and on/off from all three player
views (already fixed in 7054a4c to win the custom-action slot) is the
only equalizer control that belongs in the car. Preset selection stays on
the phone. This lands back on the redesign mockup's original rule ("sin
carpeta de ecualizador"), now for a road-tested reason. getChildren keeps
answering the folder's id transitionally, since a head unit can have the
old tree cached for a session or two.

The two "raiz always includes/ends with Ecualizador" tests are replaced,
not regressed -- same move the codebase already made once in the other
direction for the same folder.

Tests: 1127 -> 1132.

test/servicios/navegacion_auto_test.dart

@@ -238,37 +238,10 @@ void main() {
   });
 
   group('ConstructorArbolAuto.raiz', () {
-    test('con incluirMusicaLocal: true devuelve exactamente 5 carpetas no '
-        'reproducibles con los ids esperados, terminando en Ecualizador', () {
+    test('con incluirMusicaLocal: true devuelve exactamente 4 carpetas no '
+        'reproducibles con los ids esperados', () {
       final raiz = ConstructorArbolAuto().raiz(incluirMusicaLocal: true);
 
-      expect(raiz, hasLength(5));
-      final ids = raiz.map((item) => item.id).toSet();
-      expect(
-        ids,
-        equals({
-          ConstructorArbolAuto.idFavoritos,
-          ConstructorArbolAuto.idTodas,
-          ConstructorArbolAuto.idMisEmisoras,
-          ConstructorArbolAuto.idMusicaLocal,
-          ConstructorArbolAuto.idEcualizador,
-        }),
-      );
-      for (final item in raiz) {
-        expect(item.playable, isFalse);
-        expect(item.title, isNotEmpty);
-      }
-      // Decision `auto/ecualizador-diseno`: Ecualizador is always LAST,
-      // after Música Local when it is present.
-      expect(raiz[raiz.length - 2].id, ConstructorArbolAuto.idMusicaLocal);
-      expect(raiz.last.id, ConstructorArbolAuto.idEcualizador);
-    });
-
-    test('con incluirMusicaLocal: false devuelve exactamente 4 carpetas — '
-        'Música Local queda OCULTA, no vacía, y Ecualizador sigue presente y '
-        'al final', () {
-      final raiz = ConstructorArbolAuto().raiz(incluirMusicaLocal: false);
-
       expect(raiz, hasLength(4));
       final ids = raiz.map((item) => item.id).toSet();
       expect(
@@ -277,25 +250,50 @@ void main() {
           ConstructorArbolAuto.idFavoritos,
           ConstructorArbolAuto.idTodas,
           ConstructorArbolAuto.idMisEmisoras,
-          ConstructorArbolAuto.idEcualizador,
+          ConstructorArbolAuto.idMusicaLocal,
+        }),
+      );
+      for (final item in raiz) {
+        expect(item.playable, isFalse);
+        expect(item.title, isNotEmpty);
+      }
+      expect(raiz.last.id, ConstructorArbolAuto.idMusicaLocal);
+    });
+
+    test('con incluirMusicaLocal: false devuelve exactamente 3 carpetas — '
+        'Música Local queda OCULTA, no vacía', () {
+      final raiz = ConstructorArbolAuto().raiz(incluirMusicaLocal: false);
+
+      expect(raiz, hasLength(3));
+      final ids = raiz.map((item) => item.id).toSet();
+      expect(
+        ids,
+        equals({
+          ConstructorArbolAuto.idFavoritos,
+          ConstructorArbolAuto.idTodas,
+          ConstructorArbolAuto.idMisEmisoras,
         }),
       );
       expect(ids, isNot(contains(ConstructorArbolAuto.idMusicaLocal)));
-      expect(raiz.last.id, ConstructorArbolAuto.idEcualizador);
     });
 
-    test('la raíz SÍ ofrece la carpeta de ecualizador -- decisión '
-        '`auto/ecualizador-diseno` SUPERSEDE la regla anterior de "sin '
-        'carpeta de ecualizador" (commit `2403da3`); este test REEMPLAZA '
-        'deliberadamente al test homónimo previo que afirmaba lo contrario, '
-        'no es una regresión', () {
+    test('la raíz NO ofrece la carpeta de ecualizador -- decisión owner '
+        'tras conducir con ella: on/off en pantalla es el único control de '
+        'ecualizador que pertenece en el coche, la selección de preset se '
+        'queda en el móvil. Esto REEMPLAZA deliberadamente al test homónimo '
+        'previo que afirmaba lo contrario (que a su vez había reemplazado la '
+        'ausencia original en `2403da3`) -- no es una regresión, es la '
+        'segunda vuelta de la misma decisión con evidencia real de uso', () {
       final ids =
           ConstructorArbolAuto()
               .raiz(incluirMusicaLocal: true)
               .map((item) => item.id)
               .toList();
 
-      expect(ids, contains(ConstructorArbolAuto.idEcualizador));
+      expect(ids, isNot(contains(ConstructorArbolAuto.idEcualizador)));
+      // The id constant itself is NOT deleted: getChildren still answers it
+      // transitionally for a head unit with a stale cached browse tree. See
+      // servicio_audio.dart's getChildren for that courtesy branch.
       expect(ConstructorArbolAuto.idEcualizador, 'ecualizador');
     });
   });