refactor(application): migrate all queries to Stream-based API

- Replace byte[] and Base64String with required Stream PdfStream
- Simplify validators: remove XOR/Base64 validation, only check NotNull
- Affected queries: ValidatePdfQuery, ValidatePdfAQuery, CheckPdfAttachmentsQuery, ExtractSwissQrCodeQuery
- Memory efficiency: direct stream usage, no intermediate byte[] copies

DocumentOperator.Application/ValidatePdfA/Validators/ValidatePdfAQueryValidator.cs

@@ -4,45 +4,15 @@ namespace DocumentOperator.Application.ValidatePdfA.Validators;
 
 /// <summary>
 /// Validator for ValidatePdfAQuery
-/// Ensures exactly ONE input format is provided (PdfBytes XOR Base64Pdf)
+/// Ensures PdfStream is not null
 /// </summary>
 public class ValidatePdfAQueryValidator : AbstractValidator<Queries.ValidatePdfAQuery>
 {
     public ValidatePdfAQueryValidator()
     {
-        RuleFor(x => x)
-            .Must(x => (x.PdfBytes != null && x.PdfBytes.Length > 0) ^ 
-                       !string.IsNullOrWhiteSpace(x.Base64Pdf))
-            .WithMessage("Either PdfBytes or Base64Pdf must be provided, but not both");
-
-        When(x => !string.IsNullOrWhiteSpace(x.Base64Pdf), () =>
-        {
-            RuleFor(x => x.Base64Pdf!)
-                .Must(BeValidBase64)
-                .WithMessage("Base64Pdf must be a valid Base64 string");
-        });
-
-        When(x => x.PdfBytes != null, () =>
-        {
-            RuleFor(x => x.PdfBytes!)
-                .Must(bytes => bytes.Length > 0)
-                .WithMessage("PdfBytes cannot be empty");
-        });
-    }
-
-    private static bool BeValidBase64(string base64)
-    {
-        if (string.IsNullOrWhiteSpace(base64))
-            return false;
-
-        try
-        {
-            Convert.FromBase64String(base64);
-            return true;
-        }
-        catch (FormatException)
-        {
-            return false;
-        }
+        // Rule: PdfStream must be provided
+        RuleFor(x => x.PdfStream)
+            .NotNull()
+            .WithMessage("PdfStream is required");
     }
 }