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

Entities/DTO/Common/QueryParameterDto.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Entities.DTO
+{
+	public class QueryParameterDto
+	{
+		public int PageIndex { get; set; }
+		public int PageSize { get; set; }
+		public string Search { get; set; }
+	}
+}

Entities/DTO/Common/ResponseDto.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Entities.DTO
+{
+	public class ResponseDto
+	{
+		public bool IsSuccessfulRegistration { get; set; }
+		public IEnumerable<string> Errors { get; set; } = Enumerable.Empty<string>();
+	}
+}

Entities/DTO/Common/TypeCommonDto.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Entities.DTO
+{
+	public record TypeCommonDto(Guid Id, string Name);
+}

Entities/DTO/Common/TypeCommonRequest.cs

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+using Entities.Contracts;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Entities.DTO
+{
+	public record TypeCommonRequest(TypeNameType Type, Guid? SubjectId);
+}