docs(spec): register UMA Pistis pantheon placement and lane split

[mdheller]

Summary

• add a docs-first UMA Pistis pantheon registry mapping names, slugs, roles, and upstream repo placement
• add an ADR recording the ecosystem placement rules and the lane/build split
• document the complementary stack split between Argo/Tekton execution lanes and Foreman/Katello content/provisioning

Why

We needed an upstream landing point for the named local-first platform concepts without prematurely forcing all of them into normative schemas. This establishes the human-readable registry and repo boundaries so follow-on schema/API/AsyncAPI PRs can stay additive and land in the right place.

Follow-on

• additive schema/API/AsyncAPI work for MICHAEL, PRAXIS, ASHAMAAT, PHAROS/ARIADNE, IANUS, Codex, Kairos, and Shiloh
• matching runtime/integration docs in agentos-spine
• lane/build stack alignment docs in workstation-contracts