initial: add login

config/auth.ts

@@ -0,0 +1,28 @@
+import { Router } from "expo-router";
+
+let routerInstance: Router | null = null;
+
+/**
+ * Set router instance để dùng trong non-component context
+ */
+export const setRouterInstance = (router: Router) => {
+  routerInstance = router;
+};
+
+/**
+ * Handle 401 error - redirect to login
+ */
+export const handle401 = () => {
+  if (routerInstance) {
+    (routerInstance as any).replace("/login");
+  } else {
+    console.warn("Router instance not set, cannot redirect to login");
+  }
+};
+
+/**
+ * Clear router instance (optional, for cleanup)
+ */
+export const clearRouterInstance = () => {
+  routerInstance = null;
+};