Add dark theme and repair features

- Dark theme with white text for better readability
- Flush DNS, Reset TCP/IP, Reboot buttons
- ShellView.xaml: dark background, white text colors
- ShellViewModel.cs: new repair commands
- Publish settings for self-contained EXE

fix-text.ps1

@@ -0,0 +1,6 @@
+$file = 'E:\Geekanarchy\Net-Apps\EnterpriseTroubleshooter\EnterpriseTroubleshooter.sln\EnterpriseTroubleshooter\Views\ShellView.xaml'
+$content = Get-Content $file -Raw
+$content = $content.Replace('Foreground="#555"', 'Foreground="White"')
+$content = $content.Replace('Foreground="#888"', 'Foreground="White"')
+$content = $content.Replace('Foreground="#999"', 'Foreground="White"')
+Set-Content $file -Value $content -NoNewline