Refactor ResultController ctor, enhance BadRequest logging

Removed IConfiguration from ResultController constructor, now only using IMediator. Added logging for BadRequestException inner exceptions in ExceptionHandlingMiddleware for improved error diagnostics.

src/ReC.API/Middleware/ExceptionHandlingMiddleware.cs

@@ -63,6 +63,13 @@ public class ExceptionHandlingMiddleware
         switch (exception)
         {
             case BadRequestException badRequestEx:
+                if (badRequestEx.InnerException is not null)
+                {
+                    logger.LogError(
+                        badRequestEx.InnerException,
+                        "BadRequestException inner exception captured.");
+                }
+
                 context.Response.StatusCode = (int)HttpStatusCode.BadRequest;
                 details = new() 
                 {