- CONFIGURATION.md: remove Flask/SendGrid/WEBAPP_SECRET_KEY references,
update env vars to JWT_SECRET_KEY and SESSION_SECRET, point to
config/.env.template and config/instance.yaml.example
- disaster-recovery.md: rewrite for Docker volumes; cover GCP disk
snapshot backup/restore and full VM rebuild; drop systemd/nginx/SSH
- server.md: strip rsync, systemd, nginx, Linux group, and sudo
sections; keep Docker Compose operations, log viewing, health checks,
sync/admin CLI, and Jira webhook procedures