AskUserQuestionItem.detail is part of the user-interaction seam contract
but the web frame schema dropped it and the composer never rendered it
(review r3635427108). askUserQuestionItemSchema now forwards detail, the
composer renders it under the title in the description text style, and
the fixture's multi-select question carries one.
Contract face moves to contract/slots.ts (PropsRuntime composition off the
conversation SlotMap entry, flat answer/cancel injected share); apply takes
the ui-sidebar terminal form (strict need() service reads, ctx.effect-wrapped
single register, framework-resolved sessionId); tests upgrade to the terminal
style (props-direct component specs with standard-kit stubs, real-registry
apply spec with children-declared slot, fiber-teardown case).
