Fix UI helper errors during headless -Preset and -Config runs (#4941)

* Make UI helpers no-op when no window exists

The -Preset and -Config paths run Invoke-WinUtilAutoRun before the XAML
form is created and before PresentationCore is loaded, so every call into
Invoke-WPFUIThread failed with InvokeMethodOnNull and every call into
Set-WinUtilTweaksProgressIndicator failed to resolve [Windows.Visibility].
The errors were non-terminating, so tweaks still applied, but each run
filled the log with noise.

Loading presentationframework earlier does not help: Visibility lives in
PresentationCore, which only loads once a WPF object is instantiated, and
the XAML-named progress controls do not exist in these paths either.
Guarding the two helpers covers Invoke-WPFtweaksbutton, Invoke-WPFundoall
and Invoke-WPFFeatureInstall, which the existing per-call-site $hasUI
convention never reached.

* Suppress stray console output from automation runs

Invoke-WPFRunspace returns an IAsyncResult that no caller uses, and
Set-WinUtilRegistry was the only New-PSDrive call site that did not
suppress its output. A GUI click handler discards both, but the -Preset
and -Config paths call the workflows directly, so an async handle dump
and a PSDrive table landed in the user's log.

The handle itself is kept because pester/runspace.Tests.ps1 asserts that
Invoke-WPFRunspace returns a single IAsyncResult, so the suppression goes
at the four call sites reachable from Invoke-WinUtilAutoRun.

* Add project learning for window-free UI helpers

AGENTS.md

@@ -163,6 +163,7 @@ When the user corrects an agent approach, add or tighten one concrete rule here
 - Import Pester 5.8.0 before running tests so `Invoke-Pester -Output Detailed -CI` does not resolve to Windows' inbox Pester 3.4.0.
 - Keep package install/uninstall process launches simple unless explicitly requested; do not add a separate stdout/stderr process logging helper for winget or Chocolatey.
 - When the active log file is owned by `Start-Transcript`, do not call `Add-Content` against that file; write to host output so the transcript captures the line in the same log file without recording a terminating-error diagnostic.
+- Keep UI helpers such as `Invoke-WPFUIThread` and `Set-WinUtilTweaksProgressIndicator` safe to call without a window; the `-Preset` and `-Config` paths run the workflows before the form is created and before PresentationCore is loaded.
 - Log install/uninstall package names and package-manager IDs before queuing background runspace work; do not rely on runspace host output for the package identity.
 - For Win11 Creator, start each new ISO modification in a fresh `WinUtil_Win11ISO_*` temp directory; existing-work detection is only for resuming/exporting already modified media.
 - For Win11 Creator driver injection, keep offline WIM servicing to one mount, one `/Add-Driver`, and one commit; do not export editions or run unrelated WIM cleanup, and reject damaged metadata before ISO export.