feat(20-windows-client): aplikacja C# WinForms do zdalnego druku etykiet

- System tray app z NotifyIcon + ContextMenuStrip
- Polling API orderPRO (GET /api/print/jobs/pending)
- Pobieranie etykiet PDF i druk przez PdfiumViewer
- Formularz ustawień: URL API, klucz, drukarka, interwał
- Okno logów z historią (ciemny motyw, Consolas)
- Self-contained .NET 8 publish (win-x64)
- Milestone v0.7 Zdalne drukowanie etykiet — COMPLETE

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

clients/windows/OrderPROPrint/Services/PrintService.cs

@@ -0,0 +1,32 @@
+using System.Drawing.Printing;
+using PdfiumViewer;
+
+namespace OrderPROPrint.Services;
+
+public class PrintService
+{
+    public bool PrintPdf(byte[] pdfBytes, string printerName)
+    {
+        using var stream = new MemoryStream(pdfBytes);
+        using var pdfDocument = PdfDocument.Load(stream);
+
+        using var printDocument = pdfDocument.CreatePrintDocument();
+        printDocument.PrinterSettings.PrinterName = printerName;
+        printDocument.DefaultPageSettings.Margins = new Margins(0, 0, 0, 0);
+
+        // A6 = 105x148mm = 413x583 hundredths of inch
+        printDocument.DefaultPageSettings.PaperSize = new PaperSize("A6", 413, 583);
+
+        printDocument.PrintController = new StandardPrintController();
+
+        try
+        {
+            printDocument.Print();
+            return true;
+        }
+        catch
+        {
+            return false;
+        }
+    }
+}