fix: address Copilot review — z-index, Escape key, signed-out UX

- Raise header to z-50 so toggle button stays clickable above backdrop
- Use document keydown listener for Escape instead of onKeyDown on backdrop
- Only render hamburger toggle when signed in
- Make SignedOutPanel col-span responsive (col-span-1 on mobile)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/auth/SignedOutPanel.tsx

@@ -20,7 +20,7 @@ export function SignedOutPanel({
   buttonTestId,
 }: SignedOutPanelProps) {
   return (
-    <div className="col-span-2 flex min-h-[calc(100vh-64px)] items-center justify-center bg-slate-50 p-10 text-center">
+    <div className="col-span-1 md:col-span-2 flex min-h-[calc(100vh-64px)] items-center justify-center bg-slate-50 p-10 text-center">
       <div className="rounded-xl border border-slate-200 bg-white px-4 py-4 md:px-8 md:py-6 shadow-sm">
         <p className="text-sm text-slate-600">{message}</p>
         <SignInButton

frontend/src/components/templates/DashboardShell.tsx

@@ -79,11 +79,22 @@ export function DashboardShell({ children }: { children: ReactNode }) {
 
   const toggleSidebar = useCallback(() => setSidebarOpen((v) => !v), []);
 
+  // Dismiss sidebar on Escape
+  useEffect(() => {
+    if (!sidebarOpen) return;
+    const onKey = (e: KeyboardEvent) => {
+      if (e.key === "Escape") setSidebarOpen(false);
+    };
+    document.addEventListener("keydown", onKey);
+    return () => document.removeEventListener("keydown", onKey);
+  }, [sidebarOpen]);
+
   return (
     <div className="min-h-screen bg-app text-strong" data-sidebar={sidebarOpen ? "open" : "closed"}>
-      <header className="sticky top-0 z-40 border-b border-slate-200 bg-white shadow-sm">
+      <header className="sticky top-0 z-50 border-b border-slate-200 bg-white shadow-sm">
         <div className="flex items-center py-3">
           <div className="flex items-center px-4 md:px-6 md:w-[260px]">
+            {isSignedIn ? (
               <button
                 type="button"
                 className="mr-3 rounded-lg p-2 text-slate-600 hover:bg-slate-100 md:hidden"
@@ -92,6 +103,7 @@ export function DashboardShell({ children }: { children: ReactNode }) {
               >
                 {sidebarOpen ? <X className="h-5 w-5" /> : <Menu className="h-5 w-5" />}
               </button>
+            ) : null}
             <BrandMark />
           </div>
           <SignedIn>
@@ -120,10 +132,7 @@ export function DashboardShell({ children }: { children: ReactNode }) {
         <div
           className="fixed inset-0 z-40 bg-black/30 md:hidden"
           onClick={toggleSidebar}
-          onKeyDown={(e) => e.key === "Escape" && toggleSidebar()}
+          aria-hidden="true"
-          role="button"
-          tabIndex={-1}
-          aria-label="Close navigation"
         />
       ) : null}