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

lib/models/supplement_intake.dart

@@ -3,7 +3,7 @@ class SupplementIntake {
   final int supplementId;
   final DateTime takenAt;
   final double dosageTaken; // Total dosage amount taken
-  final int unitsTaken; // Number of units taken
+  final double unitsTaken; // Number of units taken (can be fractional)
   final String? notes;
 
   SupplementIntake({
@@ -32,7 +32,7 @@ class SupplementIntake {
       supplementId: map['supplementId'],
       takenAt: DateTime.parse(map['takenAt']),
       dosageTaken: map['dosageTaken'],
-      unitsTaken: map['unitsTaken'] ?? 1, // Default for backwards compatibility
+      unitsTaken: (map['unitsTaken'] ?? 1).toDouble(), // Default for backwards compatibility
       notes: map['notes'],
     );
   }
@@ -42,7 +42,7 @@ class SupplementIntake {
     int? supplementId,
     DateTime? takenAt,
     double? dosageTaken,
-    int? unitsTaken,
+    double? unitsTaken,
     String? notes,
   }) {
     return SupplementIntake(