schemas: OpenAPI provider-callback and operator

[croadfeldt]

UC map — Realizes UC-3, UC-17 (provider-callback + operator).

Implements UDLM contracts: dcm-project/udlm#20 — provider-contract + provider-callback-auth on the provider/operator OpenAPI.
Depends on the UDLM substrate landing first (Wave C); wave index: dcm-project/udlm#35.

Decision: Provider-callback and operator OpenAPI schemas.

Part of the staged croadfeldt/dcm → dcm-project/dcm upstreaming: single-concern PRs, ≤3k lines, logical boundaries. (1489 lines, 2 files.)

Draft — pending team re-engagement.

[croadfeldt]

Superseded by the ordered, scoped set (#109–#117), tracked in #108 — croadfeldt/dcm republished at parity in smaller, self-reviewable PRs; the eng-review feedback carries forward (see #108 and the UDLM carry-forward register). Nothing here is lost.