restore standard window controls, minimize-to-tray, close-exits

- Restore default FormBorderStyle (resizable with min/max/close buttons)
- Minimize button hides to tray (WindowState=Minimized -> Hide())
- Close button and tray Exit both call Shutdown() then close normally
- Tray Show/DoubleClick restores window from tray

win/gatuna-client/Program.cs

@@ -20,18 +20,19 @@ static class Program
         tray.ContextMenuStrip.Items.Add("Show", null, (_, _) =>
         {
             form.Show();
+            form.WindowState = FormWindowState.Normal;
             form.Activate();
         });
         tray.ContextMenuStrip.Items.Add("-");
         tray.ContextMenuStrip.Items.Add("Exit", null, (_, _) =>
         {
-            form.Shutdown();
             tray.Visible = false;
-            Application.Exit();
+            form.Close();
         });
         tray.DoubleClick += (_, _) =>
         {
             form.Show();
+            form.WindowState = FormWindowState.Normal;
             form.Activate();
         };