Introduce DTOs and refactor app layer to use them

Added DTO classes for Connection, Endpoint, EndpointAuth, EndpointParam, Profile, and RecAction. Updated AutoMapper profiles, DbContext, and command handlers to use DTOs instead of domain entities. This decouples the application layer from the domain model, improving maintainability and flexibility. Cleaned up some using directives and file headers.

src/ReC.Application/Common/Dto/EndpointParamDto.cs

@@ -0,0 +1,33 @@
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace ReC.Application.Common.Dto;
+
+/// <summary>
+/// Represents the TBREC_CFG_ENDPOINT_PARAMS table.
+/// All properties are nullable to provide flexibility on the database side,
+/// preventing breaking changes if columns are altered to be nullable in production.
+/// </summary>
+public record EndpointParamDto
+{
+    public long? Id { get; set; }
+
+    public bool? Active { get; set; }
+
+    public string? Description { get; set; }
+
+    public short? GroupId { get; set; }
+
+    public byte? Sequence { get; set; }
+
+    public string? Key { get; set; }
+
+    public string? Value { get; set; }
+
+    public string? AddedWho { get; set; }
+
+    public DateTime? AddedWhen { get; set; }
+
+    public string? ChangedWho { get; set; }
+
+    public DateTime? ChangedWhen { get; set; }
+}