feat(gui): carry the question detail field over the wire and render it

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.

packages/host/apiproxy/src/api/events.schema.ts

@@ -17,6 +17,7 @@ export const askUserQuestionItemSchema = z.object({
   id: z.string(),
   question: z.string(),
   header: z.string().optional(),
+  detail: z.string().optional(),
   options: z.array(z.object({ label: z.string(), description: z.string().optional() })).optional(),
   multiSelect: z.boolean().optional(),
 }) satisfies z.ZodType<Wire<AskUserQuestionItem>>