Refactor note handling to include ID generation and improve initialization logic

lib/notes.dart

@@ -1,6 +1,7 @@
 import 'package:intl/intl.dart';
 
 class Note {
+  final String id;
   final String date;
   late final String displayDate;
   String content;
@@ -9,6 +10,7 @@ class Note {
   String problemReason;
 
   Note({
+    required this.id,
     required this.date,
     required this.content,
     this.snippet,