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

app/Http/Requests/Admin/AdminUserUpdateRequest.php

@@ -0,0 +1,41 @@
+<?php
+
+namespace App\Http\Requests\Admin;
+
+use Illuminate\Validation\Rule;
+use Illuminate\Foundation\Http\FormRequest;
+
+/**
+ * 管理员用户更新请求。
+ *
+ * @see AdminUserUpdateController
+ */
+final class AdminUserUpdateRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    protected function prepareForValidation(): void
+    {
+        if ($this->input('email') === '') {
+            $this->merge(['email' => null]);
+        }
+    }
+
+    /**
+     * @return array<string, array<int, mixed>>
+     */
+    public function rules(): array
+    {
+        $adminUser = $this->route('admin_user');
+
+        return [
+            'nickname' => ['sometimes', 'string', 'max:128'],
+            'email' => ['sometimes', 'nullable', 'string', 'email', 'max:255', Rule::unique('admin_users', 'email')->ignore($adminUser?->id)],
+            'password' => ['sometimes', 'nullable', 'string', 'min:8', 'max:256'],
+            'status' => ['sometimes', 'integer', Rule::in([0, 1])],
+        ];
+    }
+}