Refactor. Add data layer

BudgetApp/Services/Models/ChartData.cs

@@ -0,0 +1,8 @@
+namespace BudgetApp.Services.Models;
+
+public class ChartData
+{
+    public List<string> Labels { get; set; } = [];
+    public List<ChartDataset> Datasets { get; set; } = [];
+    public List<List<string>> DayTransactionLabels { get; set; } = [];
+}