refactor(infrastructure): implement Stream-based PDF processing

DevExpressPdfProcessor:
- ValidateAsync, ValidatePdfAAsync, CheckAttachmentsAsync: Stream parameters
- Defensive Position=0 validation (BadRequestException for seekable streams not at beginning)
- Remove unsafe Position reset (non-seekable stream compatibility)
- Remove PdfProcessingException wrapping (let DevExpress exceptions propagate naturally)

DevExpressSwissQrCodeProcessor:
- ExtractSwissQrCodeAsync: Stream parameter
- Defensive Position=0 validation
- Remove unsafe Position reset

Memory optimization: MemoryStream.TryGetBuffer fast path for byte[] extraction

DocumentOperator.Infrastructure/Services/QrCodeProcessing/DevExpressSwissQrCodeProcessor.cs

@@ -24,19 +24,27 @@ public sealed class DevExpressSwissQrCodeProcessor : ISwissQrCodeProcessor
 
     /// <inheritdoc />
     public async Task<(Bill Bill, string[] RawLines)> ExtractSwissQrCodeAsync(
-        byte[] pdfBytes,
+        Stream pdfStream,
         int[]? pageNumbers = null,
         CancellationToken cancellationToken = default)
     {
-        if (pdfBytes.Length == 0)
-            throw new ArgumentException("PDF document contains no byte data.", nameof(pdfBytes));
+        ArgumentNullException.ThrowIfNull(pdfStream, nameof(pdfStream));
+        
+        if (pdfStream.Length == 0)
+            throw new ArgumentException("PDF stream is empty.", nameof(pdfStream));
+
+        // Defensive validation: Seekable streams must be at Position = 0
+        // Non-seekable streams (e.g., NetworkStream) are not checked
+        if (pdfStream.CanSeek && pdfStream.Position != 0)
+            throw new BadRequestException(null, new ArgumentException(
+                "PDF stream must be positioned at the beginning (Position = 0).",
+                nameof(pdfStream)));
 
         using var pdfDocument = new PdfDocumentProcessor();
-        using var pdfStream = new MemoryStream(pdfBytes);
         pdfDocument.LoadDocument(pdfStream);
 
         if (pdfDocument.Document.Pages.Count == 0)
-            throw new ArgumentException("PDF document contains no pages.", nameof(pdfBytes));
+            throw new ArgumentException("PDF document contains no pages.", nameof(pdfStream));
 
         // Determine which pages to scan
         int[] pagesToScan = DeterminePageNumbers(pdfDocument.Document.Pages.Count, pageNumbers);