SNMP health metrics using Netgear enterprise MIB (OID 4526) for
memory free/total and CPU utilization string parsing, plus IF-MIB counters.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
NetgearPlus: get_snmp_config() returns None (SNMP not accessible via HTTP API).
NetgearSmart: get_snmp_config() reads current community, fix_snmp configures
'snmp-server community public ro' via CLI.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>