refactor: add IIdentityService abstraction to Application layer

src/NexusReader.Application/Abstractions/Services/IIdentityService.cs

@@ -0,0 +1,14 @@
+using FluentResults;
+using NexusReader.Application.DTOs.User;
+
+namespace NexusReader.Application.Abstractions.Services;
+
+public interface IIdentityService
+{
+    event Func<Task>? OnStateInvalidated;
+    Task<Result> RegisterAsync(string email, string password);
+    Task<Result> LoginAsync(string email, string password, bool rememberMe = false);
+    Task<Result> LogoutAsync();
+    Task<Result<UserProfileDto>> GetProfileAsync();
+    Task<Result> RefreshTokenAsync();
+}