fix(alarm): cap the ring at the configured volume instead of the device max

The ring-scoped media override forced STREAM_MUSIC to the hardware
maximum, so the alarm's configured percentage was applied on top of a
maxed speaker: "50%" meant 50% of the phone's absolute maximum and
the fade rode against that ceiling, far louder than the device-
relative level users were used to. On-device logcat also showed the
just_audio player emitting one buffer at volume 1.0 before the 5%
pre-start took effect, a full-scale click on the maxed stream.

The stream is now capped at the alarm's configured volume (still
independent of the device's own level, so it rings at device-volume
0), and the player ramps from ~5% up to its full range under that
cap. Perceived peak is the configured fraction of the device maximum,
reached gradually; the opening click drops to the configured fraction
instead of full scale.

test/pantallas/pantalla_alarma_sonando_test.dart

@@ -205,7 +205,9 @@ void main() {
       await tester.pumpAndSettle();
 
       expect(entorno.android.detenidas, contains('ring1'));
-      expect(entorno.audio.volumenesAplicados, [0.05, 0.85]);
+      // Player ramps to its OWN full range (1.0); the configured level is
+      // enforced by the media-stream cap, not by the player target.
+      expect(entorno.audio.volumenesAplicados, [0.05, 1.0]);
     });
 
     testWidgets('si confirmar el audio con el nativo falla, el fade-in de Dart '
@@ -225,7 +227,7 @@ void main() {
       // unica fuente audible, y el ring no debe quedar pegado en
       // _volumenInicialFadeIn para siempre.
       expect(entorno.android.detenidas, isEmpty);
-      expect(entorno.audio.volumenesAplicados, [0.05, 0.85]);
+      expect(entorno.audio.volumenesAplicados, [0.05, 1.0]);
     });
   });
 
@@ -247,7 +249,7 @@ void main() {
       );
       expect(
         entorno.audio.volumenesAplicados,
-        [0.05, 0.85],
+        [0.05, 1.0],
         reason: 'el fade-in debe arrancar tambien en el camino ya-sonando',
       );
     });