style(desktop-picker): 修改桌面选择器的透明样式并添加边框

将背景色改为 fuchsia 并设置透明键，添加绘制边框的 Paint 事件处理，提升视觉效果

resources/desktop-picker.ps1

@@ -43,8 +43,18 @@ $hl.FormBorderStyle = [System.Windows.Forms.FormBorderStyle]::None
 $hl.TopMost = $true
 $hl.ShowInTaskbar = $false
 $hl.StartPosition = [System.Windows.Forms.FormStartPosition]::Manual
-$hl.BackColor = [System.Drawing.Color]::Red
+$hl.BackColor = [System.Drawing.Color]::Fuchsia
-$hl.Opacity = 0.35
+$hl.TransparencyKey = [System.Drawing.Color]::Fuchsia
+$hl.Add_Paint({
+  param($sender, $e)
+  $pen = New-Object System.Drawing.Pen([System.Drawing.Color]::FromArgb(255, 255, 32, 32), 3)
+  try {
+    $size = $sender.ClientSize
+    $e.Graphics.DrawRectangle($pen, 1, 1, ($size.Width - 3), ($size.Height - 3))
+  } finally {
+    $pen.Dispose()
+  }
+})
 function Set-ClickThrough($form) {
   if ($form.IsHandleCreated) {
     $GWL_EXSTYLE = -20