Add stamp to first page of PDF documents

Introduce functionality to add a stamp to the top-right corner of
the first page of a PDF. The stamp includes a white background,
a green border, and two lines of text: "✔ VERARBEITET" in bold
green font and the current date/time in gray font. The stamp is
drawn using `DevExpress.Pdf.PdfDocumentProcessor` and saved to
the document's foreground.

DXApp.TemplateKitProject/Services/PdfResultPackageService.cs

@@ -70,6 +70,54 @@ public class PdfResultPackageService(
                 Data = File.ReadAllBytes(reportPath)
             });
 
+            // Schritt 4: Stempel auf Seite 1 zeichnen
+            var firstPage = processor.Document.Pages[0];
+            using (var graphics = processor.CreateGraphicsWorldSystem())
+            {
+                // Stempel-Position: oben rechts
+                // Welt-Koordinaten: Ursprung oben links, X nach rechts, Y nach unten
+                var stampX = (float)firstPage.CropBox.Width - 200;
+                var stampY = 20f;
+                var stampWidth = 175f;
+                var stampHeight = 50f;
+
+                // Hintergrund weiß
+                using var whiteBrush = new DevExpress.Drawing.DXSolidBrush(
+                    System.Drawing.Color.White);
+                graphics.FillRectangle(whiteBrush,
+                    new System.Drawing.RectangleF(stampX, stampY, stampWidth, stampHeight));
+
+                // Rahmen grün
+                using var greenPen = new DevExpress.Drawing.DXPen(
+                    System.Drawing.Color.Green, 1.5f);
+                graphics.DrawRectangle(greenPen,
+                    new System.Drawing.RectangleF(stampX, stampY, stampWidth, stampHeight));
+
+                // Text Zeile 1: VERARBEITET
+                using var greenBrush = new DevExpress.Drawing.DXSolidBrush(
+                    System.Drawing.Color.Green);
+                var fontBold = new DevExpress.Drawing.DXFont(
+                    "Arial", 11, DevExpress.Drawing.DXFontStyle.Bold);
+                graphics.DrawString(
+                    "✔ VERARBEITET",
+                    fontBold,
+                    greenBrush,
+                    new System.Drawing.PointF(stampX + 8, stampY + 6));
+
+                // Text Zeile 2: Datum/Uhrzeit
+                using var grayBrush = new DevExpress.Drawing.DXSolidBrush(
+                    System.Drawing.Color.DimGray);
+                var fontNormal = new DevExpress.Drawing.DXFont("Arial", 9);
+                graphics.DrawString(
+                    DateTime.Now.ToString("dd.MM.yyyy HH:mm"),
+                    fontNormal,
+                    grayBrush,
+                    new System.Drawing.PointF(stampX + 8, stampY + 28));
+
+                graphics.AddToPageForeground(
+                    processor.Document.Pages[0], 96, 96);
+            }
+
             // Schritt 4: Speichern
             try
             {