Add released-package compatibility CI and documentation example validation

[codeforester]

Summary

Make the demo a dependable compatibility consumer for published base-cli releases.

Scope

• Test the demo against the minimum and latest supported base-cli versions.
• Run the demo against a wheel installation rather than a source checkout.
• Validate README commands and expected machine-readable output.
• Add an explicitly non-blocking or manual path for testing an upcoming base-cli release.

Acceptance criteria

• CI proves the documented quickstart on the supported Python matrix.
• Version pins and update policy are visible and reproducible.
• A compatibility failure identifies whether the issue is in the demo or the package contract.

Non-goals

Do not make the demo depend on unpublished private implementation modules.