Update and rename app.js to authService.js

Signed-off-by: Abdurhaman Mohammed Ahamed <abdurhamanmohammeda@gmail.com>

Author: abdurhamanmohammeda-a11y

Js/app.js

@@ -0,0 +1,31 @@
+
+// authService.js
+import { auth } from "./firebase.js";
+import { signInWithEmailAndPassword, signOut, onAuthStateChanged } from "firebase/auth";
+
+/**
+ * User login
+ * @param {string} email
+ * @param {string} password
+ * @returns {Promise<UserCredential>}
+ */
+export const login = (email, password) => {
+  return signInWithEmailAndPassword(auth, email, password);
+};
+
+/**
+ * User logout
+ * @returns {Promise<void>}
+ */
+export const logout = () => {
+  return signOut(auth);
+};
+
+/**
+ * Monitor auth state changes
+ * @param {function} callback - Function that receives user object (or null)
+ * @returns {unsubscribe} function to stop listening
+ */
+export const onAuthStateChange = (callback) => {
+  return onAuthStateChanged(auth, callback);
+};