Adapter protocol

Status: stub. Phase 2 deliverable.

Defines how a fork configures oxi for its own project: the 10-method Adapter protocol, the dataclasses (NamingConfig, BudgetCaps, PathsConfig, PromoteRecipe, DispatchHost, RoadmapItem), and the registration API.

Written once the adapter protocol is implemented and has been consumed by at least two adapters (_reference + _self).