[eval] Python + CLI: register eval scenarios

Part of #380
Depends on: #383

## What

Python-facing registration API and CLI command for eval scenarios.

- Extend `CardRegistry` (or add an eval-specific registry path) to support registering `EvalScenario` objects
- Support loading `EvalScenario` from a YAML/TOML file
- CLI: `opsml eval register --file eval.yaml` — reads scenario file, registers to server
- Registration should be idempotent on same scenario hash
- Works in both local and server mode

Start with the existing CardRegistry and EvalScenario paths, then inspect the opsml eval register entry point and the scenario format used by eval.yaml. Trace dependency #383 before deciding where registration belongs. Done means YAML/TOML scenarios register through the CLI in local and server modes, with repeated registration of the same scenario hash producing no duplicate.

Written by the indexing model from the issue text.