feat: rename to paperspec and add the website

- Rename manuspec to paperspec everywhere outside pixi.toml: prose, the
  tools, provenance tool names and the fixture key derivations, so every
  fixture and vector is rebuilt.
- Move the namespace addresses under the site, mirroring the repository:
  schema $id https://paperspec.scient.ing/schemas/<file>, the JSON-LD
  context https://paperspec.scient.ing/context/scienting-1.jsonld, and
  term IRIs https://paperspec.scient.ing/vocab#<term>. Format
  identifiers (scienting-*) and URNs (urn:scienting:) are unchanged.
- tools/site.py (standard library only) builds _site/: every file of the
  repository at its own path, each Markdown file rendered as a page with
  sidebar navigation, heading anchors matching the forge's, folder
  listings, a vocabulary page for the context's IRIs, a heading search
  and a 404 page; light and dark themes.
- check.py builds the site and checks that every Markdown file has a
  page, every internal link and fragment resolves, no Markdown is left
  unrendered, and every $id, the context address and the vocabulary IRIs
  are files of the site.
- deploy/: a Caddyfile with the media types and CORS the data needs, and
  a guide; .gitea/workflows/site.yml builds on main and publishes with
  rsync when the SITE_* secrets are set.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

fixtures/invalid/heading-not-first/package/roster.json

@@ -1 +1 @@
-{"format":"scienting-roster/1","keys":[{"id":"ana","person":{"name":"Ana Example"},"public":"KaptcVSRRjQ1EaRm7sWY+ExKeNtrQ5Xny7G0sOQq1Rc=","purposes":["sign"],"registered_at":"2026-09-01T00:00:00Z","revoked_at":null,"role":"owner","scheme":"ed25519"},{"id":"ben","person":{"name":"Ben Example"},"public":"FTgWcu94E4B07ky4Sd2W6VcMzamQgx8G7v++3Y/jvfY=","purposes":["sign"],"registered_at":"2026-09-01T00:00:00Z","revoked_at":null,"role":"editor","scheme":"ed25519"},{"id":"ben-spot","person":{"name":"Ben Example"},"public":"Z9Kcdd6RARODR/eUTI0yTXQkue0/K6ehrInEtAfGrzI=","purposes":["spot-check"],"registered_at":"2026-09-01T00:00:00Z","revoked_at":null,"role":"editor","scheme":"ed25519"},{"id":"cara","person":{"name":"Cara Example"},"public":"J8HPVPYtxYbKQZLMnlvND2FeGrhHj/RN8fLQ0MeyKCc=","purposes":["sign"],"registered_at":"2026-09-01T00:00:00Z","revoked_at":null,"role":"reader","scheme":"ed25519"}],"store":"smithlab"}
+{"format":"scienting-roster/1","keys":[{"id":"ana","person":{"name":"Ana Example"},"public":"RUiz5j+y0QwgOtsQpqXrlq+gy3c/JFnkxwvlWUNX4Ao=","purposes":["sign"],"registered_at":"2026-09-01T00:00:00Z","revoked_at":null,"role":"owner","scheme":"ed25519"},{"id":"ben","person":{"name":"Ben Example"},"public":"L4WMLs7xLjBLRsxS/EYpD194puMBpADybcfFEWxBkWk=","purposes":["sign"],"registered_at":"2026-09-01T00:00:00Z","revoked_at":null,"role":"editor","scheme":"ed25519"},{"id":"ben-spot","person":{"name":"Ben Example"},"public":"rkzxigjCXg869PGSFAVr4EDXXRmwk+S/+wJ93lrG4dc=","purposes":["spot-check"],"registered_at":"2026-09-01T00:00:00Z","revoked_at":null,"role":"editor","scheme":"ed25519"},{"id":"cara","person":{"name":"Cara Example"},"public":"I7J1GqG5CHOc0LHYZPNNto1Me2lJUzBVn2A7GrUGbZ4=","purposes":["sign"],"registered_at":"2026-09-01T00:00:00Z","revoked_at":null,"role":"reader","scheme":"ed25519"}],"store":"smithlab"}