Redirect app root to login when visiting /generadorexamenesllm without a session.

This fixes the blank page on the base URL by normalizing the no-trailing-slash path in nginx and redirecting unauthenticated users to /login before React mounts.

frontend/nginx.conf

@@ -50,6 +50,11 @@ server {
         try_files $uri =404;
     }
 
+    # Raíz sin barra final → login (evita pantalla en blanco por basename)
+    location = /generadorexamenesllm {
+        return 301 /generadorexamenesllm/login;
+    }
+
     location / {
         try_files $uri $uri/ /index.html;
     }