Add Playwright e2e coverage and Node 20 pin

frontend/src/components/layout/AppLayout.tsx

@@ -89,7 +89,10 @@ export function AppLayout() {
         }}
       />
 
-      <div className={cn('app-shell relative z-1', sidebarCollapsed && 'app-shell--collapsed')}>
+      <div
+        className={cn('app-shell relative z-1', sidebarCollapsed && 'app-shell--collapsed')}
+        data-testid="app-shell"
+      >
       {/* Top Bar - spans full width */}
       <TopBar />
 

frontend/src/components/scripts/PowerShellHighlighter.tsx

@@ -68,11 +68,11 @@ interface Props {
 export function PowerShellHighlighter({ script, className }: Props) {
   const parts: React.ReactNode[] = []
   let lastIndex = 0
+  const tokenRegex = new RegExp(TOKEN_REGEX.source, TOKEN_REGEX.flags)
 
-  TOKEN_REGEX.lastIndex = 0
   let match: RegExpExecArray | null
 
-  while ((match = TOKEN_REGEX.exec(script)) !== null) {
+  while ((match = tokenRegex.exec(script)) !== null) {
     if (match.index > lastIndex) {
       parts.push(script.slice(lastIndex, match.index))
     }