Tiny nginx reverse proxy for first-party Mixpanel tracking. Forks the config from
mixpanel/tracking-proxy and points
it at the EU residency endpoints (api-eu.mixpanel.com, cdn-eu.mxpnl.com).
Deployed as the mixpanel-proxy DigitalOcean App, defined in the
DigitalOcean-Global Terraform workspace. App Platform builds this Dockerfile
directly from master — no image registry involved.