[eval] EvalScenario schema + EvalRegistryRecord data model

Part of #380

## What

Define the core data model for the evaluation framework.

- `EvalScenario`: scenario definition struct — inputs, expected outputs, eval function reference, metadata, scenario hash
- `EvalRegistryRecord`: versioned registry entry linked to a `ServiceCard` (space/name/version/uid) and a Scouter record id
- DB migration for eval registry records table
- Scouter payload contract: what shape does Scouter bifrost expect for eval scenario registration

Contract types belong in `opsml-types`. DB schema goes through the standard migration path in `opsml-sql`.