[ci skip] Add platform stack (core services) for Terragrunt migration
stacks/platform/ contains 22 core/cluster services: metallb, dbaas, redis,
traefik, technitium, headscale, authentik, rbac, k8s-portal, crowdsec,
monitoring, vaultwarden, reverse-proxy, metrics-server, nvidia, kyverno,
uptime-kuma, wireguard, xray, mailserver, cloudflared, infra-maintenance.
Outputs: tls_secret_name, redis_host, postgresql_host/port, mysql_host/port,
smtp_host/port — consumed by downstream service stacks via dependency blocks.
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