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

app/Http/Requests/Admin/AdminUserStoreRequest.php

@@ -0,0 +1,59 @@
+<?php
+
+namespace App\Http\Requests\Admin;
+
+use Illuminate\Support\Str;
+use Illuminate\Foundation\Http\FormRequest;
+
+/**
+ * 管理员用户创建请求。
+ *
+ * @see AdminUserStoreController
+ */
+final class AdminUserStoreRequest extends FormRequest
+{
+    /**
+     * Determine if the user is authorized to make this request.
+     */
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    /**
+     * Prepare the data for validation.
+     */
+    protected function prepareForValidation(): void
+    {
+        $username = $this->input('username');
+        if (is_string($username)) {
+            $this->merge([
+                'username' => Str::lower(trim($username)),
+            ]);
+        }
+
+        if ($this->input('email') === '') {
+            $this->merge([
+                'email' => null,
+            ]);
+        }
+    }
+
+    /**
+     * Get the validation rules that apply to the request.
+     *
+     * @return array<string, array<int, mixed>>
+     */
+    public function rules(): array
+    {
+        return [
+            'username' => ['required', 'string', 'min:2', 'max:64', 'regex:/^[a-zA-Z0-9._-]+$/u', 'unique:admin_users,username'],
+            'nickname' => ['required', 'string', 'max:128'],
+            'email' => ['nullable', 'string', 'email', 'max:255'],
+            'password' => ['required', 'string', 'min:8', 'max:256'],
+            'status' => ['sometimes', 'integer', 'in:0,1'],
+            'role_slugs' => ['required', 'array', 'min:1'],
+            'role_slugs.*' => ['string', 'max:64', 'distinct', 'exists:admin_roles,slug'],
+        ];
+    }
+}