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.

---------

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

pester/configs.Tests.ps1

@@ -264,8 +264,9 @@ Describe "App navigation config" {
     It "is wired to an existing XAML target grid" {
         $mainScript = Get-Content -Path $script:mainScriptPath -Raw
         $tabInitializerScript = Get-Content -Path (Join-Path $script:repoRoot "functions/private/Initialize-WinUtilTabContent.ps1") -Raw
+        $uiInitializerScript = Get-Content -Path (Join-Path $script:repoRoot "functions/public/Initialize-WPFUI.ps1") -Raw
         $targetGridMatch = [regex]::Match(
-            "$mainScript`n$tabInitializerScript",
+            "$mainScript`n$tabInitializerScript`n$uiInitializerScript",
             'Invoke-WPFUIElements\s+-configVariable\s+\$sync\.configs\.appnavigation\s+-targetGridName\s+"([^"]+)"'
         )