Added budget entity

PostFundManagement.Domain/Entities/Budget.cs

@@ -0,0 +1,10 @@
+namespace PostFundManagement.Domain.Entities;
+
+public class Budget : Models.Budget
+{
+    public virtual Project? Project { get; set; }
+
+    public virtual User? Creator { get; set; }
+
+    public virtual User? Approver { get; set; }
+}