NextAuth.js v5 requires an explicit API route to expose authentication endpoints.
Added missing route handler at frontend/src/app/api/auth/[...nextauth]/route.ts that imports and exports handlers from the auth configuration.
This fixes:
- /api/auth/signin endpoint (was 404)
- /api/auth/callback endpoint
- /api/auth/session endpoint
- Frontend authentication flow initialization
Verification: Endpoint now returns HTTP 200 and frontend loads without ClientFetchError.
8643c3dfa7