Refactor supplement intake handling to support fractional units and update notification service initialization for Linux

lib/services/notification_service.dart

@@ -19,10 +19,14 @@ class NotificationService {
       requestBadgePermission: true,
       requestSoundPermission: true,
     );
+    const LinuxInitializationSettings linuxSettings = LinuxInitializationSettings(
+      defaultActionName: 'Open notification',
+    );
 
     const InitializationSettings initSettings = InitializationSettings(
       android: androidSettings,
       iOS: iosSettings,
+      linux: linuxSettings,
     );
 
     await _notifications.initialize(initSettings);