MarkLabs.pl NetGuard 0.9.0-rc.6

First public pre-release of MarkLabs.pl NetGuard.\n\nCompatible firmware pair:\n- NETGUARD-MASTER 0.9.0-rc.6 for WT32-ETH01\n- NETGUARD-POWER 0.3.1 for SONOFF 4CHR3\n- UART protocol v3 at 9600 baud, 8N1\n\nInstall or update the Power Module first, then the Master. Keep automation disabled until both controllers are updated and communication has been verified. Verify every binary against the attached SHA-256 manifests before flashing.\n\nThis is a pre-release intended for controlled validation. Read README.md, SECURITY.md, and the production checklist before deployment.