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/Queries/ValidatePdfAQuery.cs

@@ -6,19 +6,14 @@ using MediatR;
 namespace DocumentOperator.Application.ValidatePdfA.Queries;
 
 /// <summary>
-/// Query for PDF/A validation (supports both byte array and Base64 input)
+/// Query for PDF/A validation (Stream-based)
 /// </summary>
 public record ValidatePdfAQuery : IRequest<PdfAValidationResult>
 {
     /// <summary>
-    /// PDF as byte array (direct upload)
+    /// PDF as stream (caller is responsible for disposal)
     /// </summary>
-    public byte[]? PdfBytes { get; init; }
-
-    /// <summary>
-    /// PDF as Base64 string (API clients)
-    /// </summary>
-    public string? Base64Pdf { get; init; }
+    public required Stream PdfStream { get; init; }
 }
 
 /// <summary>
@@ -33,14 +28,8 @@ public class ValidatePdfAQueryHandler(IPdfProcessor PdfProcessor, IMapper Mapper
     /// </summary>
     public async Task<PdfAValidationResult> Handle(ValidatePdfAQuery request, CancellationToken cancellationToken)
     {
-        // Use byte[] if available, otherwise convert Base64
-        byte[] pdfBytes = request.PdfBytes ?? Convert.FromBase64String(request.Base64Pdf!);
-
-        // Convert to stream for IPdfProcessor
-        using var pdfStream = new MemoryStream(pdfBytes);
-
-        // Call DevExpress service (exceptions propagate naturally)
-        var metadata = await PdfProcessor.ValidatePdfAAsync(pdfStream);
+        // Call DevExpress service directly with stream (exceptions propagate naturally)
+        var metadata = await PdfProcessor.ValidatePdfAAsync(request.PdfStream);
 
         // Map DTO to response DTO using AutoMapper
         return Mapper.Map<PdfAValidationResult>(metadata);

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");
     }
 }