Write the OpenAPI docs in the API templates as attributes and drop doctrine/annotations #597

Summary

Write the OpenAPI documentation in the shipped API module templates as PHP attributes (#[OA\...]) instead of @OA\... annotations, and remove the abandoned doctrine/annotations package. Part of the PHP 8.1 update (#595).

Why

Composer reports doctrine/annotations as abandoned, with no replacement. It is kept only because the OpenAPI docs use annotations, and zircote/swagger-php reads annotations only when that package is installed (it is a suggestion there, not a requirement). The 3.0.3 changelog notes that it stays "on the PHP 8.0 baseline", because swagger-php's attribute scanning needs PHP 8.1. With 8.1 as the minimum, that reason is gone.

Current state

• 7 template files under src/Module/Templates (DefaultApi and DemoApi, in Controllers/OpenApi) use @OA\... annotations. None use attributes.
• OpenApiCommand generates the spec with Generator::scan().
• doctrine/annotations is required in composer.json and not imported in src.

Proposed change

• Convert the annotations in those templates to #[OA\...] attributes.
• Check that the generated spec is the same as before for the same API.
• Remove doctrine/annotations from composer.json.
• Describe the change for existing projects in the changelog and the upgrade guide.

Breaking changes

• A project whose own controllers carry @OA\... annotations (for example generated from the earlier templates) loses its OpenAPI output once doctrine/annotations is gone. It has to convert its annotations to attributes. This needs a clear upgrade note.

Out of scope

• Changing the API documentation content.
• Upgrading zircote/swagger-php.

Acceptance criteria

• the templates use attributes only and php qt generates the same OpenAPI spec as before
• doctrine/annotations is no longer required
• composer test, composer cs:check, composer phpstan and composer rector:check pass
• the upgrade note explains how to convert annotations

Notes

Relevant code: src/Module/Templates/DefaultApi, src/Module/Templates/DemoApi, src/Console/Commands/OpenApiCommand.php, composer.json.