feat: WU completion indicators - lock screen + desktop file

When X9-WindowsUpdate finds no more updates:
- Creates "! WU HOTOVO yyyy-MM-dd HH:mm.txt" on C:\Users\Public\Desktop
- Locks the workstation via one-shot task running as adminx9
  (login screen = unambiguous visual signal for the operator)
- One-shot lock task self-deletes after 5 minutes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/12-windows-update.ps1

@@ -106,11 +106,30 @@ $updates = Get-WindowsUpdate -AcceptAll -IgnoreReboot
 if ($updates) {
     Install-WindowsUpdate -AcceptAll -IgnoreReboot | Out-File "C:\Windows\Setup\Scripts\wu-pass-$(Get-Date -Format 'yyyyMMdd-HHmmss').log" -Encoding UTF8
 } else {
-    # No more updates - disable autologon and remove this task
+    # No more updates - disable autologon and clean up
     $wl = "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon"
     Set-ItemProperty -Path $wl -Name "AutoAdminLogon" -Value "0" -Type String -Force
     Remove-ItemProperty -Path $wl -Name "DefaultPassword"   -ErrorAction SilentlyContinue
     Remove-ItemProperty -Path $wl -Name "AutoLogonCount"    -ErrorAction SilentlyContinue
+
+    # Leave a visible marker on the shared Desktop so the operator knows it's done
+    $ts      = Get-Date -Format "yyyy-MM-dd HH:mm"
+    $doneMsg = "Windows Update dokoncen: $ts`r`nStroj je plne aktualizovan a pripraven k predani klientovi."
+    [System.IO.File]::WriteAllText(
+        "C:\Users\Public\Desktop\! WU HOTOVO $ts.txt",
+        $doneMsg,
+        [System.Text.Encoding]::UTF8
+    )
+
+    # Lock the workstation - login screen = clear visual signal for the operator.
+    # Runs as adminx9 (interactive session) via a one-shot task, self-deletes after 5 min.
+    $lockAction    = New-ScheduledTaskAction -Execute "rundll32.exe" -Argument "user32.dll,LockWorkStation"
+    $lockTrigger   = New-ScheduledTaskTrigger -Once -At (Get-Date).AddSeconds(5)
+    $lockPrincipal = New-ScheduledTaskPrincipal -UserId "adminx9" -LogonType Interactive -RunLevel Limited
+    $lockSettings  = New-ScheduledTaskSettingsSet -DeleteExpiredTaskAfter (New-TimeSpan -Minutes 5)
+    Register-ScheduledTask -TaskName "X9-WUDoneLock" -Action $lockAction -Trigger $lockTrigger `
+        -Principal $lockPrincipal -Settings $lockSettings -Force -ErrorAction SilentlyContinue | Out-Null
+
     Unregister-ScheduledTask -TaskName "X9-WindowsUpdate" -Confirm:$false
 }
 '@