Refactor navbar and remove legacy API/context

Replaces HomeNav with a new SiteNav and associated CSS module, updating navigation structure and user menu. Removes legacy API client, downloader, user model, and UserContext in favor of a new AuthContext stub for future authentication logic. Also cleans up HeroCarousel and minor CSS fixes.

frontend/src/layouts/HomeLayout.tsx

@@ -1,11 +1,18 @@
 import Footer from "../components/Footer/footer";
 import { Outlet } from "react-router";
-import SiteNav from "../components/navbar/SiteNav";
+import SiteNav, { type User } from "../components/navbar/SiteNav";
+
+
+const userexists: User = {
+  username: "Bruno",
+  email: "",
+  avatarUrl: "",
+};
 
 export default function HomeLayout(){
     return(
         <>
-            <SiteNav />
+            <SiteNav user={userexists} onLogin={() => {}} onLogout={() => {}} />
             <Outlet />
             <Footer />
         </>