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/Forms/LogForm.cs

@@ -0,0 +1,88 @@
+namespace OrderPROPrint.Forms;
+
+public partial class LogForm : Form
+{
+    private static LogForm? _instance;
+    private static readonly List<string> _logEntries = new();
+    private static readonly object _logLock = new();
+
+    public LogForm()
+    {
+        InitializeComponent();
+    }
+
+    public static void Log(string message)
+    {
+        var entry = $"[{DateTime.Now:HH:mm:ss}] {message}";
+
+        lock (_logLock)
+        {
+            _logEntries.Add(entry);
+            if (_logEntries.Count > 500)
+                _logEntries.RemoveAt(0);
+        }
+
+        if (_instance != null && !_instance.IsDisposed)
+        {
+            try
+            {
+                _instance.Invoke(() => _instance.AppendLog(entry));
+            }
+            catch { }
+        }
+    }
+
+    public static void ShowInstance()
+    {
+        if (_instance == null || _instance.IsDisposed)
+        {
+            _instance = new LogForm();
+
+            lock (_logLock)
+            {
+                foreach (var entry in _logEntries)
+                {
+                    _instance.AppendLog(entry);
+                }
+            }
+        }
+
+        _instance.Show();
+        _instance.BringToFront();
+    }
+
+    private void AppendLog(string text)
+    {
+        txtLog.AppendText(text + Environment.NewLine);
+    }
+
+    private void BtnClear_Click(object sender, EventArgs e)
+    {
+        txtLog.Clear();
+        lock (_logLock)
+        {
+            _logEntries.Clear();
+        }
+    }
+
+    private void BtnCopy_Click(object sender, EventArgs e)
+    {
+        if (!string.IsNullOrEmpty(txtLog.Text))
+        {
+            Clipboard.SetText(txtLog.Text);
+        }
+    }
+
+    protected override void OnFormClosing(FormClosingEventArgs e)
+    {
+        if (e.CloseReason == CloseReason.UserClosing)
+        {
+            e.Cancel = true;
+            Hide();
+        }
+        else
+        {
+            base.OnFormClosing(e);
+        }
+    }
+}