Implement attachment detection in ValidatePDF

Updated PHASENPLAN.md and ROADMAP.md to reflect a complete restructuring of the development plan and added a "Bugfix: Attachment Detection" entry.

Implemented attachment detection in DevExpressPdfProcessor.cs using the new `DetectEmbeddedFiles` method, which scans raw PDF data for the `/EmbeddedFiles` keyword. Updated the `hasAttachments` property to use this method and set `attachmentCount` to `-1` when attachments are detected.

Added a new test, `ValidateAsync_PdfWithoutAttachments_ReturnsNoAttachments`, in DevExpressPdfProcessorTests.cs to verify that PDFs without attachments are correctly identified. Included a note about future testing for PDFs with attachments using ZUGFeRD files.

All related tests are passing (12/12 green).

DocumentOperator.Infrastructure/Services/PdfProcessing/DevExpressPdfProcessor.cs

@@ -41,10 +41,12 @@ public class DevExpressPdfProcessor : IPdfProcessor
             int pageCount = document.Pages.Count;
             string pdfVersion = document.Version.ToString(); // z.B. "1.4", "1.7"
 
-            // Attachments - TODO: Implement in Phase 6 (ExtractAttachments Feature)
-            // DevExpress PdfDocument API might need different approach for attachments
-            bool hasAttachments = false;
-            int attachmentCount = 0;
+            // Attachments (embedded files)
+            // DevExpress PdfDocument API doesn't expose EmbeddedFiles directly.
+            // We use a simple PDF raw data scan for "/EmbeddedFiles" keyword.
+            // This is a pragmatic approach until Feature 2 (ExtractAttachments) is implemented.
+            bool hasAttachments = DetectEmbeddedFiles(pdfBytes);
+            int attachmentCount = hasAttachments ? -1 : 0; // -1 = "has attachments, count unknown"
 
             // 4. Create and return PdfMetadata Value Object (fully qualified name!)
             return new DocumentOperator.Domain.Models.ValueObjects.PdfMetadata(
@@ -63,4 +65,29 @@ public class DevExpressPdfProcessor : IPdfProcessor
                 ex);
         }
     }
-}
+
+    /// <summary>
+    /// Detects embedded files in PDF by scanning raw PDF data for /EmbeddedFiles keyword.
+    /// This is a pragmatic approach as DevExpress PdfDocument API doesn't expose EmbeddedFiles directly.
+    /// </summary>
+    /// <param name="pdfBytes">PDF raw bytes</param>
+    /// <returns>True if PDF contains /EmbeddedFiles keyword in proper context, false otherwise</returns>
+    private static bool DetectEmbeddedFiles(byte[] pdfBytes)
+    {
+        // PDF embedded files are declared in the document catalog:
+        // /Names << /EmbeddedFiles << /Names [...] >> >>
+        // We search for the pattern "/Names" followed by "/EmbeddedFiles"
+
+        string pdfText = System.Text.Encoding.ASCII.GetString(pdfBytes);
+
+        // Look for the specific PDF dictionary pattern: /Names and /EmbeddedFiles
+        // This is more precise than just searching for /EmbeddedFiles alone
+        int namesIndex = pdfText.IndexOf("/Names", StringComparison.Ordinal);
+        if (namesIndex == -1)
+            return false;
+
+        // Check if /EmbeddedFiles appears after /Names within reasonable distance (< 1000 chars)
+        int embeddedFilesIndex = pdfText.IndexOf("/EmbeddedFiles", namesIndex, Math.Min(1000, pdfText.Length - namesIndex), StringComparison.Ordinal);
+        return embeddedFilesIndex > namesIndex;
+    }
+}