fix: repair popup install binding, dialog titles, presets switch, radio groups, JSON, tests (#4893)

* fix: repair popup install binding, dialog titles, presets switch, radio groups, JSON, tests

- Invoke-WPFInstall: add param block so the right-click app popup binds
  -PackagesToInstall. It previously dropped the argument into $args and
  installed the whole selected list instead of the clicked app (or warned
  that nothing was selected).
- Replace undefined $AppTitle with "WinUtil" in Install/UnInstall warning
  boxes, matching the XAML window title and sibling dialogs.
- tweaks.json: remove stray nested "link" inside the WPFToggleScrollbars
  registry entry (dead property; registry entries expose only the six
  consumed fields).
- Invoke-WPFPresets: fix dead switch cases to the wildcard-pattern
  convention so selectedFeatures/selectedToggles clear correctly.
- Invoke-WPFUIElements: store the group StackPanel in radioButtonGroups so
  grouped radio buttons share one container (else branch was unreachable).
- sanity.Tests.ps1: pass the Windows PowerShell parser script via
  -EncodedCommand; -Command string marshaling corrupted backticks/quotes and
  produced false parse failures.
- install-workflow.Tests.ps1: remove the AppTitle workaround and update
  title assertions to "WinUtil"; drop orphaned cleanup lines.
- Add CHANGES.md with technical and plain-language explanations.

Verified: each bug reproduced against HEAD, fixes demonstrated to change
behavior, full Pester suite 471/471.

* Delete

* test: cover the explicit popup install parameter path

Add a regression test invoking Invoke-WPFInstall -PackagesToInstall with a
package different from the default sync.selectedApps selection and assert
the runspace receives the explicit object, mirroring the Initialize-WPFUI
popup call shape. Existing default-path coverage is unchanged.

functions/public/Invoke-WPFUIElements.ps1

@@ -327,6 +327,7 @@ function Invoke-WPFUIElements {
                             $groupStackPanel = New-Object Windows.Controls.StackPanel
                             $groupStackPanel.Orientation = "Vertical"
                             [System.Windows.Automation.AutomationProperties]::SetName($groupStackPanel, $entryInfo.GroupName)
+                            $radioButtonGroups[$entryInfo.GroupName] = $groupStackPanel
 
                             # Add the group container to the ItemsControl
                             $itemsControl.Items.Add($groupStackPanel) | Out-Null