Hardening OTBR

Part 1 got OTBR running as a non-root user with three capabilities. Part 2 covers the hardening block in the service file — what each directive does, why one had to be an exception, and how to use systemd-analyze security as a decision tool rather than a score to chase. Part 2 of 2.

OpenThread Border Router assumes it runs as root. Getting it down to a least-privilege non-root user means figuring out exactly what it needs — which turned out to be a source code problem, not a trial-and-error problem. Part 1 of 2.