The Buzz adapter's check_requirements() reads config from env only, so a
config.yaml-only setup (relay URL in gateway.platforms.buzz.extra) failed the
check_fn gate and was silently skipped at startup. Add an apply_yaml_config_fn
hook that bridges buzz.extra -> BUZZ_* env vars, mirroring the Slack/Telegram
pattern; BUZZ_PRIVATE_KEY stays a .env secret.
Also fix send_reaction() to use buzz-cli's real flags (--event <id> --emoji),
replacing the non-existent --channel/--message-id flags that would have failed
on every message. Verified live against the hosted relay (accepted:true).
Refs #68871
01f8852ccc