Implement the Crucible.Stage behaviour across all deployment stages to
support the describe/1 contract required by crucible_framework 0.5.0.
This enables stage introspection and schema-driven pipeline validation.

Stage implementations updated:
- Deploy: Schema with target, strategy, and config options
- Promote: Schema for deployment promotion to full traffic
- Rollback: Schema for version rollback operations

Deploy stage supports inference targets vLLM, TGI, Triton, SageMaker,
and Kubernetes with rollout strategies canary, blue_green, rolling,
and recreate.

Added comprehensive conformance test suite validating:
- All stages export describe/1 callback
- Schemas contain required fields (name, description, required, optional)
- Type specifications cover all declared fields
- No overlap between required and optional field lists
- Type specs conform to canonical type system

Dependency updates:
- crucible_framework ~> 0.4.0 to ~> 0.5.0 (describe/1 contract)
- crucible_ir ~> 0.2.0 to ~> 0.2.1
- crucible_model_registry ~> 0.1.0 to ~> 0.2.0

Documentation expanded with stage options reference and usage examples.