Fix login API endpoint path by removing redundant 'admin/' prefix

internal/web/templates/admin/login.html

@@ -57,7 +57,7 @@
 function login() {
     const password = document.getElementById('password').value;
 
-    fetch('admin/api/login', {
+    fetch('api/login', {
         method: 'POST',
         headers: {
             'Content-Type': 'application/json'