docs(web-ui/agent): fix stale /answer-question/{id} → /api/answer-question/{id}

Both loose-ends flyout and ask-bind prose referenced the bare path
without the /api/ prefix. The code was fixed in 98b5e976 to use the
correct path; dashboard.md already documents it correctly as
POST /api/answer-question/{id}. Align agent.md to match.

docs/web-ui/agent.md

@@ -154,7 +154,7 @@ After the drain the inbox list empties on reload (the filter is
 `acked_at IS NULL`, so drained messages disappear). Loose-ends flyout: questions,
 approvals, and reminders pending against this agent (`GET /api/loose-ends`);
 question rows carry an inline answer form that POSTs cross-origin to
-the core dashboard's `/answer-question/{id}` so the operator answers
+the core dashboard's `POST /api/answer-question/{id}` so the operator answers
 *as operator* (see `docs/boundary.md`). Tasks flyout: in-flight bash
 tasks (`GET /api/bash-tasks`); each row shows status (`▶ running` /
 `◷ queued`), the task id, elapsed time, and a truncated one-line
@@ -172,7 +172,7 @@ the slot list and pairs each unbound slot with the first unclaimed
 pending operator-bound question whose `question` text matches the
 slot's stashed `_askQuestion`. On match the slot mounts the
 `buildAnswerForm` (same form shape as the loose-ends flyout —
-POSTs to the core's `/answer-question/{id}` cross-origin). Slots
+POSTs to the core's `POST /api/answer-question/{id}` cross-origin). Slots
 stay in the array after binding so the reconciler can flip them
 to a neutral `[resolved]` tag when the question later disappears
 from the pending list. Disappearance can mean answered, cancelled