feat(auth): implement user authentication with JWT and NextAuth

- Added user registration and login functionality with JWT authentication.
- Created auth controller, service, and module in the backend.
- Implemented user model and user products management.
- Integrated NextAuth for session management on the frontend.
- Added middleware for protecting routes and handling public access.
- Updated frontend API routes to include authorization headers.
- Enhanced recipe and user product models to support ownership and visibility.
- Created registration and login pages in the frontend.
- Added necessary types for NextAuth session management.

frontend/middleware.ts

@@ -0,0 +1,25 @@
+import { NextResponse } from 'next/server';
+import { auth } from './auth';
+
+export default auth((req) => {
+  const { pathname } = req.nextUrl;
+
+  // Alltid tillgängliga sidor
+  const publicPaths = ['/login', '/register'];
+  if (publicPaths.some((p) => pathname.startsWith(p))) {
+    return NextResponse.next();
+  }
+
+  // Om ej inloggad, omdirigera till /login
+  if (!req.auth) {
+    const loginUrl = new URL('/login', req.url);
+    loginUrl.searchParams.set('callbackUrl', pathname);
+    return NextResponse.redirect(loginUrl);
+  }
+
+  return NextResponse.next();
+});
+
+export const config = {
+  matcher: ['/((?!_next/static|_next/image|favicon.ico|api/auth).*)'],
+};