Telegram channel — posts message to a chat via sendMessage.
:bot_token(required) — token, or{:system, "VAR"}.:chat_id(required) — chat id, or{:system, "VAR"}.:http— injected(url, json -> {:ok, status} | {:error, term}); production defaults toReq.
Missing token/chat ⇒ {:error, :not_configured} (never raises).