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/ConnectionDto.cs

@@ -0,0 +1,32 @@
+namespace ReC.Application.Common.Dto;
+
+public record ConnectionDto
+{
+    public short? Id { get; set; }
+
+    public string? Bezeichnung { get; set; }
+
+    public string? SqlProvider { get; set; }
+
+    public string? Server { get; set; }
+
+    public string? Datenbank { get; set; }
+
+    public string? Username { get; set; }
+
+    public string? Password { get; set; }
+
+    public string? Bemerkung { get; set; }
+
+    public bool? Aktiv { get; set; }
+
+    public string? ErstelltWer { get; set; }
+
+    public DateTime? ErstelltWann { get; set; }
+
+    public string? GeandertWer { get; set; }
+
+    public DateTime? GeaendertWann { get; set; }
+
+    public bool? SysConnection { get; set; }
+}