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/lazy-tabs.Tests.ps1

@@ -8,12 +8,10 @@ BeforeAll {
     function Invoke-WPFUIElements {
         param($configVariable, [string]$targetGridName, [int]$columncount)
     }
-    function Initialize-WPFUI {
-        param([string]$TargetGridName)
-    }
     function Invoke-WinUtilISOCheckExistingWork { }
     function Reset-WPFCheckBoxes { param([bool]$doToggles) }
 
+    . (Join-Path $script:repoRoot "functions\public\Initialize-WPFUI.ps1")
     . (Join-Path $script:repoRoot "functions\private\Initialize-WinUtilTabContent.ps1")
 }
 
@@ -41,9 +39,7 @@ Describe "Initialize-WinUtilTabContent" {
         Initialize-WinUtilTabContent -TabName "Install"
         Initialize-WinUtilTabContent -TabName "Install"
 
-        Should -Invoke -CommandName Invoke-WPFUIElements -Times 1 -Exactly -ParameterFilter {
-            $targetGridName -eq "appscategory" -and $columncount -eq 1
-        }
+
         Should -Invoke -CommandName Initialize-WPFUI -Times 1 -Exactly -ParameterFilter {
             $TargetGridName -eq "appscategory"
         }
@@ -105,6 +101,32 @@ Describe "Initialize-WinUtilTabContent" {
     }
 }
 
+Describe "Initialize-WPFUI" {
+    BeforeEach {
+        $script:sync = [Hashtable]::Synchronized(@{
+            configs = @{
+                appnavigation = [pscustomobject]@{}
+            }
+        })
+
+        Mock Invoke-WPFUIElements { throw "App category rendered" }
+    }
+
+    AfterEach {
+        Remove-Variable -Name sync -Scope Script -ErrorAction SilentlyContinue
+    }
+
+    It "renders app navigation through the app category target" {
+        { Initialize-WPFUI -TargetGridName "appscategory" } | Should -Throw "App category rendered"
+
+        Should -Invoke -CommandName Invoke-WPFUIElements -Times 1 -Exactly -ParameterFilter {
+            $configVariable -eq $script:sync.configs.appnavigation -and
+            $targetGridName -eq "appscategory" -and
+            $columncount -eq 1
+        }
+    }
+}
+
 Describe "Startup lazy tab wiring" {
     It "builds only install tab content before first paint" {
         $mainScript = Get-Content -Path (Join-Path $script:repoRoot "scripts\main.ps1") -Raw