fix: thread accountId through subagent announce delivery

Co-authored-by: Adam Holt <adam91holt@users.noreply.github.com>

src/utils/account-id.ts

@@ -0,0 +1,5 @@
+export function normalizeAccountId(value?: string): string | undefined {
+  if (typeof value !== "string") return undefined;
+  const trimmed = value.trim();
+  return trimmed || undefined;
+}