refactor(api): remove generic exception handling from middleware

Remove FormatException/ArgumentException handling:
- These are framework exceptions, not application-specific
- May come from internal libraries (false positives for 400 Bad Request)
- Controllers now wrap Base64 conversion with BadRequestException explicitly

Remove PdfProcessingException handling:
- Exception type removed (obsolete)
- DevExpress exceptions now propagate naturally → 500 Internal Server Error

Current exception mapping:
- ValidationException (FluentValidation) → 400 Bad Request
- BadRequestException (custom) → 400 Bad Request
- NotFoundException (custom) → 404 Not Found
- SwissQrCodeNotFoundException (custom) → 404 Not Found
- All others → 500 Internal Server Error

DocumentOperator.API/Middleware/ExceptionHandlingMiddleware.cs

@@ -1,5 +1,4 @@
 using DocumentOperator.Domain.Common.Exceptions;
-using DocumentOperator.Domain.Exceptions;
 using FluentValidation;
 using Microsoft.AspNetCore.Mvc;
 using System.Net;
@@ -67,7 +66,7 @@ public class ExceptionHandlingMiddleware(RequestDelegate Next)
                 }
             ),
 
-            // Not Found Exception (404 Not Found)
+            // Bad Request Exception (400 Bad Request)
             BadRequestException badReqEx => (
                 HttpStatusCode.BadRequest,
                 new ProblemDetails
@@ -93,19 +92,6 @@ public class ExceptionHandlingMiddleware(RequestDelegate Next)
                 }
             ),
 
-            // Swiss QR Code Not Found Exception (404 Not Found)
-            SwissQrCodeNotFoundException qrNotFoundEx => (
-                HttpStatusCode.NotFound,
-                new ProblemDetails
-                {
-                    Type = "https://datatracker.ietf.org/doc/html/rfc7231#section-6.5.4",
-                    Title = "Swiss QR Code Not Found",
-                    Status = (int)HttpStatusCode.NotFound,
-                    Detail = qrNotFoundEx.Message,
-                    Instance = context.Request.Path
-                }
-            ),
-
             // Generic Exception (500 Internal Server Error)
             _ => (
                 HttpStatusCode.InternalServerError,