The site is served at /UOR-Framework/ on GitHub Pages but all internal
links and asset references were root-relative (e.g. /css/style.css),
causing CSS, JS, and navigation to fail with 404.

Solution: read PUBLIC_BASE_PATH env var (default "") in the website
generator and prepend it to every internal URL. CI sets
PUBLIC_BASE_PATH=/UOR-Framework so the generated site resolves
correctly at https://uor-foundation.github.io/UOR-Framework/.

Changes:
- website/src/extractor.rs: namespace_summaries, build_search_index,
  and all breadcrumb helpers accept base_path parameter
- website/src/nav.rs: build_nav(base_path) prefixes all nav URLs
- website/src/renderer.rs: render_page, render_homepage,
  render_search_page accept base_path for CSS/JS/hero links
- website/src/search.rs: search_js(base_path) and
  generate_search_index(base_path) accept base_path
- website/src/lib.rs: reads PUBLIC_BASE_PATH from env, wires through
- conformance/src/validators/website/links.rs: strips PUBLIC_BASE_PATH
  prefix when resolving root-relative links against public/ dir
- .github/workflows/ci.yml, release.yml: set PUBLIC_BASE_PATH env on
  website generation and conformance steps

Conformance suite: 50/50 passed with PUBLIC_BASE_PATH=/UOR-Framework.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>