feat: establish legacy parity migration baseline

scripts/Test-LegacyParityWeb.ps1

@@ -0,0 +1,45 @@
+#Requires -Version 5.1
+
+[CmdletBinding()]
+param([string] $NodePath)
+
+Set-StrictMode -Version Latest
+$ErrorActionPreference = 'Stop'
+
+if ([string]::IsNullOrWhiteSpace($NodePath)) {
+    $command = Get-Command node -CommandType Application -ErrorAction SilentlyContinue |
+        Select-Object -First 1
+    if ($null -ne $command) {
+        $NodePath = $command.Source
+    }
+    else {
+        $bundledNode = Join-Path $env:USERPROFILE `
+            '.cache\codex-runtimes\codex-primary-runtime\dependencies\node\bin\node.exe'
+        if (Test-Path -LiteralPath $bundledNode -PathType Leaf) {
+            $NodePath = $bundledNode
+        }
+    }
+
+    if ([string]::IsNullOrWhiteSpace($NodePath)) {
+        throw 'Node.js was not found. Pass an absolute executable path with -NodePath.'
+    }
+}
+
+if (-not [IO.Path]::IsPathRooted($NodePath) -or
+    -not (Test-Path -LiteralPath $NodePath -PathType Leaf)) {
+    throw 'NodePath must identify an existing absolute node executable.'
+}
+
+$repositoryRoot = [IO.Path]::GetFullPath((Join-Path $PSScriptRoot '..'))
+$appScript = Join-Path $repositoryRoot 'src\MBN_STOCK_WEBVIEW.LegacyParityApp\Web\app.js'
+$testFile = Join-Path $repositoryRoot 'tests\LegacyParityWeb\thin-client.test.cjs'
+
+& $NodePath --check $appScript
+if ($LASTEXITCODE -ne 0) {
+    throw "Legacy parity JavaScript syntax validation failed with exit code $LASTEXITCODE."
+}
+
+& $NodePath --test $testFile
+if ($LASTEXITCODE -ne 0) {
+    throw "Legacy parity Web tests failed with exit code $LASTEXITCODE."
+}