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/MainForm.cs

@@ -17,9 +17,6 @@ public partial class MainForm : Form
         Text = "gatuna";
         Width = 520;
         Height = 380;
-        FormBorderStyle = FormBorderStyle.FixedSingle;
-        MaximizeBox = false;
-        MinimizeBox = false;
         StartPosition = FormStartPosition.CenterScreen;
         InitializeComponents();
 
@@ -146,14 +143,19 @@ public partial class MainForm : Form
         }
     }
 
+    protected override void OnResize(EventArgs e)
+    {
+        base.OnResize(e);
+        if (WindowState == FormWindowState.Minimized)
+        {
+            Hide();
+            WindowState = FormWindowState.Normal;
+        }
+    }
+
     protected override void OnFormClosing(FormClosingEventArgs e)
     {
-        if (e.CloseReason == CloseReason.UserClosing)
-        {
-            e.Cancel = true;
-            Hide();
-            return;
-        }
+        Shutdown();
         base.OnFormClosing(e);
     }