Fixed authentication protocol version downgrade vulnerability (CVE-2025-62349) by adding `minimum_auth_version` configuration option (default: 3) to prevent minions from bypassing security features through protocol downgrade attacks.

**BREAKING CHANGE:** The default value enforces authentication protocol version 3 or higher. If upgrading a deployment with older minions that do not support protocol v3, you must temporarily set `minimum_auth_version: 0` in the master configuration before upgrading the master, then upgrade all minions before removing this override.
