refactor：拆分 API 路由与请求校验，统一 final 类和代码风格

app/Http/Requests/Admin/AdminUserRoleSyncRequest.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace App\Http\Requests\Admin;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+/**
+ * 管理员用户角色同步请求。
+ *
+ * @see AdminUserRoleSyncController
+ */
+final class AdminUserRoleSyncRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    /**
+     * @return array<string, array<int, mixed>>
+     */
+    public function rules(): array
+    {
+        return [
+            'role_slugs' => ['required', 'array', 'min:1'],
+            'role_slugs.*' => ['string', 'max:64', 'distinct', 'exists:admin_roles,slug'],
+        ];
+    }
+}