Follow up to: #3576100 **Description:** `AiContextSelector::select()` is the primary programmatic API for selecting and rendering AI Context items. Before RC1, this should be exposed through an interface so contrib modules and custom integrations can depend on a stable contract instead of the concrete service class. Proposed scope: - Add `Drupal\ai_context\Service\AiContextSelectorInterface`. - Define `select(AiContextRequest $request): AiContextResult`. - Have `AiContextSelector` implement the interface. - Add a service alias for the interface in `ai_context.services.yml`. - Update internal constructor type hints and docs where appropriate. - Add or adjust test coverage confirming the service is available through the interface. This should be completed before RC1 because the public API surface becomes harder to change after stable release.