HKUDS OpenHarness Insecure Default Remote Channel Allowlist

HKUDS OpenHarness prior to PR #147 remediation contains an insecure default configuration vulnerability where remote channels inherit allow_from = ["*"] permitting arbitrary remote senders to pass admission checks. Attackers who can reach the configured channel can bypass access controls and reach host-backed agent runtimes, potentially leading to unauthorized file disclosure and read access through default-enabled read-only tools.