User authentication implemented

Closes #5 (closed)

public/js/app.js

+// Obtener referencia a los elementos del DOM
+const taskList = document.querySelector('.task-list ul');
+const newTaskForm = document.querySelector('form');
+
+// Logout
+document.getElementById('logout-btn').addEventListener('click', async () => {
+  try {
+    const res = await fetch('/api/users/logout', { method: 'POST' });
+    if (res.ok) {
+      window.location.href = 'login.html'; 
+    } else {
+      console.error('Logout failed');
+    }
+  } catch (err) {
+    console.error('Error during logout:', err);
+  }
+});
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