add typing for userList and change userId parameter type

src/routes/(angemeldet)/user-management/+page.svelte

@@ -8,7 +8,7 @@
 
     let userName = $state('')
     let userPassword = $state('')
-    let userList = $state([])
+    let userList: { userId: string; userName: string }[] = $state([])
     let addUserError = $state(false);
     let addUserSuccess = $state(false);
     const currentUser: string = data.user.id;
@@ -65,7 +65,7 @@
         }, 5000);
     }
 
-    async function deleteUser(userId: number) {
+    async function deleteUser(userId: string) {
         const URL = `/api/users/${userId}`;
 
         const response = await fetch(URL, {