refactor: move database-related projects to separate folder

SqlData/Application/Cqrs/Campus/Queries/GetCampusBasicInfoList/CampusBasicInfoDto.cs

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+namespace Mirea.Api.DataAccess.Application.Cqrs.Campus.Queries.GetCampusBasicInfoList;
+
+/// <summary>
+/// Represents basic information about a campus.
+/// </summary>
+public class CampusBasicInfoDto
+{
+    /// <summary>
+    /// The unique identifier for the campus.
+    /// </summary>
+    public int Id { get; set; }
+
+    /// <summary>
+    /// The code name associated with the campus.
+    /// </summary>
+    public required string CodeName { get; set; }
+
+    /// <summary>
+    /// The full name of the campus.
+    /// </summary>
+    public string? FullName { get; set; }
+}

SqlData/Application/Cqrs/Campus/Queries/GetCampusBasicInfoList/CampusBasicInfoVm.cs

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+using System.Collections.Generic;
+
+namespace Mirea.Api.DataAccess.Application.Cqrs.Campus.Queries.GetCampusBasicInfoList;
+
+/// <summary>
+/// Represents a view model containing basic information about multiple campuses.
+/// </summary>
+public class CampusBasicInfoVm
+{
+    /// <summary>
+    /// The list of campus basic information.
+    /// </summary>
+    public IList<CampusBasicInfoDto> Campuses { get; set; } = new List<CampusBasicInfoDto>();
+}

SqlData/Application/Cqrs/Campus/Queries/GetCampusBasicInfoList/GetCampusBasicInfoListQuery.cs

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+using MediatR;
+
+namespace Mirea.Api.DataAccess.Application.Cqrs.Campus.Queries.GetCampusBasicInfoList;
+
+public class GetCampusBasicInfoListQuery : IRequest<CampusBasicInfoVm>;

SqlData/Application/Cqrs/Campus/Queries/GetCampusBasicInfoList/GetCampusBasicInfoListQueryHandler.cs

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+using MediatR;
+using Microsoft.EntityFrameworkCore;
+using Mirea.Api.DataAccess.Application.Interfaces.DbContexts.Schedule;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Mirea.Api.DataAccess.Application.Cqrs.Campus.Queries.GetCampusBasicInfoList;
+
+public class GetCampusBasicInfoListQueryHandler(ICampusDbContext dbContext) : IRequestHandler<GetCampusBasicInfoListQuery, CampusBasicInfoVm>
+{
+    public async Task<CampusBasicInfoVm> Handle(GetCampusBasicInfoListQuery request, CancellationToken cancellationToken)
+    {
+        var dtos = await dbContext.Campuses.Select(c => new CampusBasicInfoDto()
+        {
+            Id = c.Id,
+            CodeName = c.CodeName,
+            FullName = c.FullName
+        }).ToListAsync(cancellationToken);
+
+        return new CampusBasicInfoVm
+        {
+            Campuses = dtos
+        };
+    }
+}