fix: correct Clerk auth.protect() usage in middleware

The auth parameter in clerkMiddleware is of type AuthFn, which has
protect() as a direct method. No need to call auth() first.

Changed: await auth().protect() → await auth.protect()

This fixes TypeScript error:
Property 'protect' does not exist on type 'Promise<SessionAuthWithRedirect>'

Verified with: npm run typecheck (passes cleanly)

Author: frankbria

frontend/src/middleware.ts

@@ -19,7 +19,7 @@ export default clerkMiddleware(async (auth, req) => {
 
   // Enforce authentication for protected routes
   // This will redirect unauthenticated users to the sign-in page
-  await auth().protect();
+  await auth.protect();
 
   return NextResponse.next();
 });