Add Mattermost Team Edition deployment (PVC, Service, NetworkPolicy),
DNS records (chat.fxhnt.ai, mail.fxhnt.ai), Tailscale nginx proxy
server block with WebSocket upgrade support, and Mattermost egress
rules to all 5 Argo workflow NetworkPolicies for exit handler webhooks.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
