[eval] Python + CLI: register eval scenarios

[thorrester]

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