Clarify the Profiles subtitle about private keys

frontend/src/screens/ProfilesScreen.tsx

@@ -66,7 +66,8 @@ export function ProfilesScreen({ onCreateProfile }: ProfilesScreenProps) {
           <div>
             <h1>Profiles</h1>
             <p className="page-subtitle">
-              Your private keys never appear here — they stay on this computer.
+              Your private keys stay on this computer and are only shown if you choose to reveal one
+              — with your vault password when it's protected.
             </p>
           </div>
           <Button variant="primary" onClick={onCreateProfile}>