fix: use h-dvh instead of h-screen to fix iOS Safari bottom cutoff

100vh on iOS Safari includes browser chrome, cutting off page content.
dvh (dynamic viewport height) adjusts correctly as the toolbar appears/disappears.

Authored by: Jack Levy

frontend/components/shared/AuthGuard.tsx

@@ -42,7 +42,7 @@ export function AuthGuard({ children }: { children: React.ReactNode }) {
 
   // Authenticated or guest browsing: render the full app shell
   return (
-    <div className="flex h-screen bg-background">
+    <div className="flex h-dvh bg-background">
       {/* Desktop sidebar — hidden on mobile */}
       <div className="hidden md:flex">
         <Sidebar />