implement SearchUsers use case

backend/app/User/UseCases/SearchUsers/SearchUsers.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace App\User\UseCases\SearchUsers;
+
+use App\Exceptions\BadRequestException;
+use App\User\User;
+use App\User\UserRepository;
+
+class SearchUsers
+{
+    public function __construct(
+        private UserRepository $userRepo,
+    ) {}
+
+    /**
+     * @return User[]
+     *
+     * @throws BadRequestException
+     */
+    public function execute(SearchUsersRequest $request): array
+    {
+        $query = trim($request->query);
+        if ($query === '') {
+            throw new BadRequestException('query is required');
+        }
+
+        return $this->userRepo->search($query);
+    }
+}

backend/app/User/UseCases/SearchUsers/SearchUsersRequest.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace App\User\UseCases\SearchUsers;
+
+class SearchUsersRequest
+{
+    public function __construct(
+        public string $query,
+    ) {}
+}