Refactor. Add data layer

BudgetApp.Data/Interfaces/IAccountRepository.cs

@@ -0,0 +1,14 @@
+using BudgetApp.Data.Entities;
+
+namespace BudgetApp.Data.Interfaces;
+
+public interface IAccountRepository
+{
+    Task<List<Account>> GetAccountsAsync(string userId);
+    Task<Account?> GetAccountAsync(int id, string userId);
+    Task CreateAccountAsync(Account account);
+    Task UpdateAccountAsync(Account account);
+    Task UpdateBalanceAsync(int id, string userId, decimal newBalance);
+    Task UpdateAccountDetailsAsync(int id, string userId, string name, string color, string currencyCode);
+    Task DeleteAccountAsync(int id, string userId);
+}