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.

lib/main.dart

@@ -12,6 +12,10 @@ import 'tema/pluriwave_tokens.dart';
 
 const _anchoMinimoLandscape = 600.0;
 
+/// Branded monochrome status-bar icon, replacing the default full-color
+/// launcher silhouette fallback.
+const androidNotificationIconResource = 'drawable/ic_stat_pluriwave';
+
 /// S5-R8: media notification accent uses the brand color, not the M3
 /// default purple. Top-level const so tests can assert it.
 const configuracionAudioService = AudioServiceConfig(
@@ -20,6 +24,7 @@ const configuracionAudioService = AudioServiceConfig(
   androidNotificationOngoing: true,
   androidStopForegroundOnPause: true,
   notificationColor: PluriWaveTokens.brand,
+  androidNotificationIcon: androidNotificationIconResource,
 );
 
 Future<void> main() async {