feat(profile): let users design their public profile

src/App.jsx

@@ -57,7 +57,8 @@ function App() {
         <TooltipProvider>
             {/* isolate: the background layer sits behind the content but in front of this div's own background. */}
             <div className="isolate min-h-screen flex flex-col bg-background text-foreground font-sans">
-                {isAuthenticated && <PageBackground appid={appearance.backgroundAppid}/>}
+                {/* A public profile shows the owner's background instead. */}
+                {isAuthenticated && !location.pathname.startsWith('/u/') && <PageBackground appid={appearance.backgroundAppid}/>}
                 <AppHeader isAuthenticated={isAuthenticated} onLogout={handleLogout}/>
 
                 <main className="grow flex flex-col">