feat: chat reactions

components/layout/site-header.tsx

@@ -26,6 +26,7 @@ import Link from "next/link";
 import { ReadingSettings } from "@/components/reading-settings";
 import { NotificationBell } from "@/components/layout/notification-bell";
 import { useAuth } from "@/components/auth/auth-provider";
+import { useHidesAppChrome } from "@/lib/use-chrome-visibility";
 
 export function SiteHeader() {
   const { user, loading } = useAuth();
@@ -33,6 +34,10 @@ export function SiteHeader() {
   // auth check we treat `loading` as anonymous so the gear doesn't flash
   // in and out — once auth resolves, it hides for signed-in users.
   const showMobileGear = !loading && !user;
+  // A chat thread has its own header — back button, name, avatar — so the
+  // wordmark bar would stack a second title above it.
+  const hidden = useHidesAppChrome();
+  if (hidden) return null;
 
   return (
     <header className="sticky top-0 z-30 bg-background/60 backdrop-blur-md">