DisallowUnknownFields rejected real Telegram payloads (entities, from,
date, etc. that our minimal structs don't cover). Lenient decode is the
right default for an upstream webhook we don't control.
Aligns the project name with the public URL (tg.arcodange.fr) and the
Arcodange organization conventions. The 'homelab-gateway' name was too
generic.
Touches: chart name + helpers, image registry path, Go module path,
secret/configmap names, deployment mountPath, all docs.
