feat(registry): add description field and interactive compose generation

[acorn421]

Summary

Add a description field to CRS registry YAML files and provide a way for users to generate compose files by selecting from registered CRSs with descriptions.

Description

Currently, registry YAML files (registry/<crs-name>.yaml) only contain name, type, and source fields. There is no short description to help users understand what each CRS does when selecting one.

Additionally, there is no CLI command to create a compose file from the registry. The existing gen-compose command only remaps CPUs on an already-written template — users must manually write the compose YAML from scratch, referencing docs/registry.md to figure out which CRSs are available and what they do.

Beyond oss-crs itself, crsbench also benefits from this: when generating experiment configs, a one-line CRS description would help users understand what each CRS does without having to look up documentation separately.

Current Status

• Registry YAML schema: name, type, source only — no description
• No CLI command to list registered CRSs
• No CLI command to generate a compose file from the registry (gen-compose only remaps CPUs on an existing template)
• CRS descriptions exist only in docs/registry.md as a hand-maintained table

Proposed Solution

• Add a description field to registry YAML files
• Add a CLI command to list registered CRSs with their descriptions and types
• Add a compose generation flow that lets users pick CRSs from the registry interactively
• Expose descriptions so crsbench can display them during experiment config creation

[acorn421]

One more thing: why do we have a bug-fixing-ensemble type? Do we need to differentiate it from regular CRS types?