Fix legacy json import compatibility, UI sidebar refactor, and improved test coverage (#4911)

* Fix backward compatibility for old-style JSON config imports

* Refactor sidebar UI generation and add tests for Get-WinUtilVariables

* Fix appnavigation config test following UI generation refactor

* Restore global sync state in variables tests

* fix(impex): migrate supported legacy selections

Keep modern imports strict while allowing legacy backups to skip retired entries with clear logging and user feedback. Add fixtures covering partial and all-retired imports.

* test: strengthen UI and global state coverage

Exercise app category rendering through Initialize-WPFUI and restore global sync without leaking test state.

* fix(impex): ignore legacy metadata fields

Limit legacy selection migration to supported WPF key families so unrelated string metadata does not produce false retired-setting warnings.

* docs: clarify legacy config imports

Distinguish strict modern flat imports from partial legacy object migration, including single-setting export shape and historical groups.

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Co-authored-by: Chris Titus <contact@christitus.com>

functions/public/Initialize-WPFUI.ps1

@@ -7,10 +7,7 @@ function Initialize-WPFUI {
 
     switch ($TargetGridName) {
         "appscategory"{
-            # TODO
-            # Switch UI generation of the sidebar to this function
-            # $sync.ItemsControl = Initialize-InstallAppArea -TargetElement $TargetGridName
-            # ...
+            Invoke-WPFUIElements -configVariable $sync.configs.appnavigation -targetGridName "appscategory" -columncount 1
 
             # Create and configure a popup for displaying selected apps
             $selectedAppsPopup = New-Object Windows.Controls.Primitives.Popup