Adds discord.py, python-telegram-bot, slack-bolt, and other messaging
platform libraries to the default Hermes derivation. This is required
for Discord/Slack/Telegram channel integration in k3s-deployed agents.
The [all] extras group stopped including messaging on 2026-05-12
(switched to lazy-install), but our Nix-built container images have
no pip available for runtime lazy installation.
Closes#2
