Fix login: don't intercept 401 on auth/login itself

A failed login attempt was triggering the global 401 interceptor which
silently redirected back to /login, making the form appear broken.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/api/index.js

@@ -11,7 +11,7 @@ api.interceptors.request.use((config) => {
 api.interceptors.response.use(
   (res) => res,
   (err) => {
-    if (err.response?.status === 401) {
+    if (err.response?.status === 401 && !err.config?.url?.includes("/auth/login")) {
       localStorage.removeItem("token");
       window.location.href = "/login";
     }