feat: migrate evaluator service from ark core

[dwmkerr]

Summary

The evaluator feature is being removed from the Ark core repository (see mckinsey/agents-at-scale-ark PR for the removal). The evaluator service needs to be migrated into the marketplace as a pluggable module.

What needs migrating

• Evaluator service (services/ark-evaluator/) — Python service that runs evaluations against query results
• CRDs: Evaluation and Evaluator custom resource definitions
• Controllers: evaluation and evaluator reconciliation controllers
• Webhooks: admission webhooks for evaluation/evaluator resources
• API endpoints: /evaluations and /evaluators REST API routes
• CLI commands: ark evaluation command group
• Dashboard pages: evaluation listing, detail, editor pages and components
• Integration tests: 8 chainsaw test suites
• Documentation: developer guide, reference docs, samples
• Samples: evaluation demos and examples

Acceptance criteria

• Evaluator is installable as a marketplace module
• Evaluator CRDs are registered by the module (not by core Ark)
• Evaluator works with the current Ark version after core removal
• Documentation is self-contained within the marketplace module
• Integration tests pass in isolation