chore: simplify spec build and publishing

[muscariello]

Summary

• move the spec build to a single uv-managed dependency source using pyproject.toml and uv.lock
• remove obsolete build artifacts and scripts, including build-spec.sh, requirements-spec.txt, and the checked-in specification/ai-catalog-respec.html
• point the published specification metadata to GitHub Pages and simplify the GitHub Actions workflow and related docs

Validation

• uv run --locked python tools/build_spec.py specification/ai-catalog.md dist/index.html --config specification/respec-config.json

[darrelmiller]

Let's remove this file, now everything is in the single specification file.