Rewrite v7 find-user-by-identity tutorial

[arhimede]

Audit finding C7. The tutorial was still a v5 page: every class, namespace and API in it is gone.

Verified against dotkernel/api branch 7.0 at 45ad282.

What was wrong

Docs said	Code says
$app->get('/user/' . $id, UserHandler::class, 'user.view')	$routeCollector->group('/user/' . $id)->get('', GetUserResourceHandler::class, 'user::view-user')
UserHandler with a get() method	GetUserResourceHandler with handle()
use Api\App\Handler\HandlerTrait;	no such trait — extend Api\App\Handler\AbstractHandler
use Api\App\Message;	Core\App\Message
use Api\User\Entity\User;	Core\User\Entity\User
(new BadRequestException())->setMessages([...])	setMessages() exists nowhere
throw new NotFoundException(Message::USER_NOT_FOUND)	NotFoundException::create(...)
UserRole::ROLE_GUEST	UserRoleEnum::Guest->value
test asserts $messages['error']['messages'][0]	problem details, so detail
dot-notation route names, three-column route:list	:: names, four-column table

What the page does now

It follows the endpoint it claims to follow. In v7 GetUserResourceHandler never queries the database — ResourceProviderMiddleware reads the #[Resource] attribute off handle() and loads the entity. So the new endpoint is one attribute:

#[Resource(entity: User::class, identifier: 'identity', placeholder: 'identity')]

which the middleware turns into findOneBy(['identity' => ...]), throwing NotFoundException itself when nothing matches. The old page's BadRequestException branch was unreachable in any version — /user/ matches no route.

Also corrected:

• Registration needs two entries, not one: factories and delegators => [HandlerDelegatorFactory::class]. Without the delegator, $responseFactory stays null and createResponse() fails.
• Why the route goes last is now the real reason: /user/{id} is UUID-constrained and {identity} is not, so a UUID matches both; static paths like /user/role were never at risk.
• MetadataMap needs no new entry — _links.self still points at /user/{uuid}.
• Tests assert the problem details body, with the two 404s explained (unmatched route vs. thrown exception).

markdownlint clean, one sentence per line.