v2.3.2-coder-answer-endpoint: fix ask_user_input submit in CoderPane

The CoderPane runs its own inference runner and broker on the boocoder
service. The AskUserInputCard was calling /api/chats/:id/answer_user_input
on the main BooChat server, which has a different inference runner — the
answer was accepted but the next turn was enqueued on the wrong runner,
so nothing happened.

Fix: register the same answer_user_input endpoint on the boocoder, and
add an apiPrefix prop to AskUserInputCard so the CoderPane routes
through /api/coder/chats/:id/answer_user_input. BooChat's MessageList
continues to use the default (no prefix) path.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/src/components/panes/CoderMessageList.tsx

@@ -230,6 +230,7 @@ export function CoderMessageList({ messages, chatId, footer }: Props) {
                   toolCall={item.run.call}
                   toolResult={item.run.result}
                   chatId={chatId}
+                  apiPrefix="/api/coder"
                 />
               );
             }