refactor(api): migrate controllers to Stream API with Base64 validation

PdfValidationController:
- ValidateFromFile: IFormFile.OpenReadStream() direct usage (no byte[] copy)
- ValidateFromBase64: try-catch Convert.FromBase64String → BadRequestException
- ValidatePdfAFromFile: IFormFile.OpenReadStream() direct usage
- ValidatePdfAFromBase64: try-catch Convert.FromBase64String → BadRequestException

PdfAttachmentController:
- CheckAttachmentsFromBase64: try-catch Convert.FromBase64String → BadRequestException

SwissQrCodeController:
- ExtractFromBase64: try-catch Convert.FromBase64String → BadRequestException

All controllers: Add using DocumentOperator.Domain.Common.Exceptions for BadRequestException

DocumentOperator.API/Controllers/PdfAttachmentController.cs

@@ -1,5 +1,6 @@
 using DocumentOperator.Application.CheckPdfAttachments.Queries;
 using DocumentOperator.Application.Common.DTOs;
+using DocumentOperator.Domain.Common.Exceptions;
 using MediatR;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc;
@@ -33,13 +34,11 @@ public class PdfAttachmentController(IMediator mediator) : ControllerBase
         IFormFile file,
         CancellationToken cancellationToken)
     {
-        // Convert IFormFile to byte array
-        using var memoryStream = new MemoryStream();
-        await file.CopyToAsync(memoryStream, cancellationToken);
-        byte[] pdfBytes = memoryStream.ToArray();
+        // Use IFormFile stream directly (no intermediate byte[] conversion)
+        using var pdfStream = file.OpenReadStream();
 
         // Send query to MediatR (ValidationBehavior runs automatically)
-        var query = new CheckPdfAttachmentsQuery { PdfBytes = pdfBytes };
+        var query = new CheckPdfAttachmentsQuery { PdfStream = pdfStream };
         var result = await mediator.Send(query, cancellationToken);
 
         return Ok(result);
@@ -64,8 +63,21 @@ public class PdfAttachmentController(IMediator mediator) : ControllerBase
         [FromBody] CheckPdfAttachmentsRequest request,
         CancellationToken cancellationToken)
     {
+        // Convert Base64 to stream (wrap in try-catch to throw BadRequestException)
+        byte[] pdfBytes;
+        try
+        {
+            pdfBytes = Convert.FromBase64String(request.Base64Pdf);
+        }
+        catch (FormatException ex)
+        {
+            throw new BadRequestException("Invalid Base64 format: " + ex.Message);
+        }
+        
+        using var pdfStream = new MemoryStream(pdfBytes);
+        
         // Send query to MediatR (ValidationBehavior runs automatically)
-        var query = new CheckPdfAttachmentsQuery { Base64Pdf = request.Base64Pdf };
+        var query = new CheckPdfAttachmentsQuery { PdfStream = pdfStream };
         var result = await mediator.Send(query, cancellationToken);
 
         return Ok(result);