Refactor AppController: return JSON on root endpoint for uptime monitoring stability

Fix Landing page: replace <a href> with <Link> to prevent full reloads and 404 errors

Add GET /courses endpoint in CoursesService and CoursesController

Fix Landing page: replace <a href> with <Link> to prevent full reloads and 404 errors

Fix Register and Login pages: add React Router navigation after login/register to redirect user to /courses

Refactor App.tsx: remove duplicate BrowserRouter/AuthProvider to fix router nesting issue

Fix App.tsx: wrap AuthProvider inside BrowserRouter to enable useNavigate

Fix main.tsx: wrap App with BrowserRouter and AuthProvider for routing and auth context

Fix AuthContext: use React Router navigation for login/logout redirects

Enhance AuthContext: persist user, store token, add login/logout redirects

Improve Register page: add debug logs for register/login responses

Move vercel.json into frontend app so Vercel rewrites work

Fix API helper: ensure prod frontend calls Render backend via VITE_API_URL

Backend config: updated CORS whitelist to include local dev, current Vercel domain, and future clean domain

Fix: added Vercel rewrite rules for React Router SPA