feat(notifications): add branded monochrome icon and color to all notifications

Replace generic system icons (info bubble, stock alarm clock) with a
custom equalizer-bars vector drawable across all 4 notification
builders: pre-notice, snooze countdown, ringing alarm, and the audio
player. Apply the app's cyan brand color to the 3 alarm notifications
that previously had none. Audio notification now explicitly declares
its icon instead of falling back to the full-color launcher icon,
which Android was auto-silhouetting into an illegible status-bar
blob.

test/tema/notification_color_test.dart

@@ -13,4 +13,15 @@ void main() {
       isNot(const Color(0xFF6750A4)),
     );
   });
+
+  test('AudioServiceConfig usa el icono monocromo de marca', () {
+    expect(
+      configuracionAudioService.androidNotificationIcon,
+      'drawable/ic_stat_pluriwave',
+    );
+    expect(
+      configuracionAudioService.androidNotificationIcon,
+      isNot('mipmap/ic_launcher'),
+    );
+  });
 }