重构项目结构，移除Assignment相关功能，优化Submission模块

Entities/DTO/Authentication/UserForAuthenticationDto.cs

@@ -0,0 +1,12 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Entities.DTO
+{
+	public class UserForAuthenticationDto
+	{
+		[Required(ErrorMessage = "Email is required")]
+		public string? Email { get; set; }
+		[Required(ErrorMessage = "Password is required")]
+		public string? Password { get; set; }
+	}
+}