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))
     }

frontend/src/pages/LoginPage.tsx

@@ -86,7 +86,7 @@ export function LoginPage() {
           </p>
         </div>
 
-        <form onSubmit={handleSubmit} className="mt-8 space-y-6">
+        <form onSubmit={handleSubmit} className="mt-8 space-y-6" data-testid="login-form">
           <div className="glass-card-static p-6 space-y-4">
             {(error || localError) && (
               <div className="rounded-[10px] border border-rose-500/20 bg-rose-500/10 p-3 text-sm text-rose-400">
@@ -146,6 +146,7 @@ export function LoginPage() {
             <button
               type="submit"
               disabled={isLoading}
+              data-testid="login-submit"
               className={cn(
                 'w-full rounded-[10px] px-4 py-2.5 text-sm font-semibold',
                 'bg-gradient-brand text-brand-dark shadow-lg shadow-primary/20 hover:opacity-90 active:scale-[0.97]',