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/App.tsx

@@ -3,7 +3,7 @@ import Home from "./pages/home/home";
 import HomeLayout from "./layouts/HomeLayout";
 import Downloader from "./pages/downloader/Downloader";
 import PrivateRoute from "./routes/PrivateRoute";
-import { UserContextProvider } from "./context/UserContext";
+//import { UserContextProvider } from "./context/UserContext";
 
 // Pages
 import PortfolioPage from "./pages/portfolio/PortfolioPage";
@@ -14,7 +14,7 @@ import ScrollToTop from "./components/common/ScrollToTop";
 export default function App() {
   return (
     <Router>
-      <UserContextProvider>
+      {/* <UserContextProvider> */}
         <ScrollToTop />
         <Routes>
           {/* Public routes */}
@@ -35,7 +35,7 @@ export default function App() {
             </Route>
           </Route>
         </Routes>
-      </UserContextProvider>
+      {/* </UserContextProvider> */}
     </Router>
   );
 }