[AshishJii]

(to be checked after #611)

What

Adds POST /wp-notifications/v1/notifications so authenticated users can queue a notification by message ID.

Why

The controller had GET and PUT but no way to create notifications via the API.

How

A CREATABLE route accepts a required id param (message ID). The controller builds a Notification using the factory with the given message ID and get_current_user_id(), then calls repository->add().

Testing

npx wp-env run tests-cli -- /var/www/html/wp-content/plugins/wp-feature-notifications/vendor/bin/phpunit --configuration=/var/www/html/wp-content/plugins/wp-feature-notifications/phpunit.xml.dist

Closes #375