fix: use plain axios for getUsers (public endpoint, avoid JWT interceptor)

frontend/lib/api.ts

@@ -108,7 +108,8 @@ export const inventoryApi = {
 
   // Users
   getUsers: async () => {
-    const res = await axiosInstance.get('/users/');
+    // [C-01] Public endpoint — use plain axios to avoid JWT interceptor
+    const res = await axios.get(`${getBackendUrl()}/users/`);
     return res.data;
   },