Add tenant/customer/instance concepts to docker-compose

[JSONbored]

Problem: The self-host docker-compose stack has zero concept of tenant, customer, or instance identity anywhere — every service name and volume is singular and unparameterized.

Area: ORB / Fleet ops

Proposal: Introduce an instance-identity variable threaded through service names, volumes, and network names, defaulting to today's single-instance behavior when unset.

Deliverables:

• A compose file that can run more than one named instance on the same host without collision, while remaining a no-op change for today's single-instance self-hosters.

[linear-code]

JSO-3556