feat(web): add nested subagent conversations

packages/client/ui-question/tests/question-composer.spec.tsx

@@ -26,6 +26,7 @@ const seatOver = (dict: Record<string, string>, common: Record<string, string>):
  *  the composed props type mandates delivery of the rest (framework hooks are
  *  plain stubs per the client testing discipline). */
 const kit = {
+  subagentReadOnly: false,
   sessionId: SID,
   useSession: (() => { throw new Error('unused') }) as unknown as SnapshotSelectorHook<ConversationSnapshot>,
   useSessions: (() => { throw new Error('unused') }) as unknown as SnapshotSelectorHook<SessionListState>,