feat: publish indexed static asset site

[jrepp]

Summary

• replace the schema-only Pages deployment with an indexed static site for schemas, templates, version metadata, and reports
• generate frontmatter JSON schemas from Pydantic models and publish template assets under stable URLs
• add Python conformance and pip-audit security reports to the Pages artifact

Validation

• uv run --python 3.12 python scripts/build_static_site.py
• python3 -m json.tool site/reports/python-conformance.json
• python3 -m json.tool site/reports/security-summary.json
• python3 -m xml.etree.ElementTree site/sitemap.xml
• uv run --python 3.12 ruff format --check scripts/build_static_site.py
• uv run --python 3.12 ruff check scripts/build_static_site.py
• local pip-audit smoke test with exported third-party requirements