release: publish base-cli 0.5.1 with metadata guardrails

[codeforester]

Closes #457

Summary

• prepare base-cli 0.5.1 with corrected release-facing documentation and base-cli-demo 0.2.0 dependency references
• add pre-tag README/version validation and exact wheel/sdist README metadata checks
• bind the release BOM to the README hash and verify PyPI metadata before creating the GitHub Release
• add regression coverage and keep the release validation aggregate green

Validation

• full tests/full_validate.sh passed locally
• package build, twine check, release metadata validation, and clean-wheel install passed
• focused guardrail tests, Ruff, and git diff --check passed

The tag will be created only after this PR is merged and hosted checks are green.