Expose JSON:API includes so callers can hydrate tags and other relationships

[PeteBishwhip]

Fixes #228.

Querying a server or a site through the SDK returned an empty relationships block and no way to hydrate related resources such as tags. Two things were missing:

1. server() and organizationSite() did not accept a $query argument, so callers could not pass ?include=tags (or any other JSON:API include).
2. Even when the API returned an included document, the SDK only consumed the top-level data envelope and discarded included, so relationship identifiers stayed unresolved.

Changes

• server(string $organizationSlug, int $serverId, array $query = []) - new $query parameter, forwarded to the API.
• organizationSite(string $organizationSlug, int $siteId, array $query = []) - same treatment.
• Resource now exposes public array $included (populated from the response) and a small included(string $name): array helper that resolves relationships[$name].data pointers against the shared included document. Handles array, single-object, and null relationship shapes.
• Forge::newResource(), Forge::transformCollection(), Forge::paginatedCollection(), and CursorPaginator::nextPage() thread the included document through to hydrated resources so it is available on collection items too.
• New included() helper tests cover: server with tag includes, site with tag includes, site with a single-object relationship (latestDeployment) plus a null server relationship, and a paginated server collection propagating the shared included document.
• README gets a short "Including Related Resources" section under Basic Usage; CHANGELOG has an [Unreleased] entry referencing Tags missing from a response when I query a resource #228.

Usage

$server = $forge->server($organizationSlug, $serverId, ['include' => 'tags']);

foreach ($server->included('tags') as $tag) {
    echo $tag['attributes']['name'];
}

The same pattern works on organizationSite() and on collection methods like servers() / serverSites().

Testing

4 new tests added

[PeteBishwhip]

Based on https://forge.laravel.com/docs/api-reference/relationships