feat: implement auth state management with RouteGuards

frontend/src/components/RouteGuards.tsx

@@ -0,0 +1,38 @@
+import { Navigate, useLocation } from "react-router-dom";
+import { ROUTES } from "../config/routes";
+import { useAuth } from "../hooks/useAuth";
+import SplashScreen from "./SplashScreen";
+
+/**
+ * Post-login routes.
+ * Redirects to /login if not already authenticated.
+ */
+export function ProtectedRoute({ children }: { children: React.ReactNode }) {
+  const { isAuthenticated, isInitializing } = useAuth();
+  const location = useLocation();
+
+  if (isInitializing) return <SplashScreen />;
+
+  if (!isAuthenticated) {
+    // Save the intended location to redirect back after login
+    return <Navigate to="/login" state={{ from: location }} replace />;
+  }
+
+  return <>{children}</>;
+}
+
+/**
+ * Pre-login flows.
+ * Redirects to /drawer if already authenticated.
+ */
+export function PublicRoute({ children }: { children: React.ReactNode }) {
+  const { isAuthenticated, isInitializing } = useAuth();
+
+  if (isInitializing) return <SplashScreen />;
+
+  if (isAuthenticated) {
+    return <Navigate to={ROUTES.DRAWER} replace />;
+  }
+
+  return <>{children}</>;
+}