Add an ecosystem-of-CLIs showcase after platform contracts stabilize

[codeforester]

Summary

Extend the demo to show how multiple CLIs could declare identity, capabilities, output contracts, and conformance evidence once the Base-CLI ecosystem platform is implemented.

Scope

• Define the learning objective and boundary for an ecosystem showcase.
• Add multiple small consumer fixtures only after the relevant metadata and conformance contracts are versioned.
• Demonstrate discovery, inspection, and compatibility evidence without making the flagship app depend on a Catalog service.

Acceptance criteria

• The feature is based on released and documented Base-CLI contracts.
• The showcase distinguishes declared metadata from observed conformance.
• Existing quickstart and core demo remain runnable without ecosystem infrastructure.

Dependencies and gate

Wait for the Base-CLI platform specification, ownership boundaries, and black-box conformance suite to stabilize. This issue is intentionally not a prerequisite for the first demo release.