Adds Prompt option to device naming mode

Introduces an explicit "Prompt" option for device naming to allow technicians to enter the device name during deployment. This replaces the implicit legacy behavior, providing clear UI controls and validation to ensure that Unattend.xml is copied, which is required for prompt-based naming. Relevant documentation is updated to reflect this new workflow capability.

FFUDevelopment/FFUUI.Core/FFUUI.Core.Config.psm1

@@ -472,7 +472,10 @@ function Update-UIFromConfig {
     if ($ConfigContent.PSObject.Properties.Name -contains 'DeviceNamingMode') {
         $deviceNamingMode = [string]$ConfigContent.DeviceNamingMode
     }
-    if ($deviceNamingMode -notin @('None', 'Template', 'Prefixes')) {
+    if ($deviceNamingMode -eq 'Legacy') {
+        $deviceNamingMode = 'Prompt'
+    }
+    if ($deviceNamingMode -notin @('None', 'Prompt', 'Template', 'Prefixes')) {
         $deviceNamingMode = 'None'
     }
     Set-DeviceNamingMode -State $State -Mode $deviceNamingMode