Add educational censorship-resistance quiz as a native Astro page

Reworks the standalone-HTML quiz from PR #7 into the site's real
architecture so it actually ships and respects every project rule.

- /quiz, /fr/quiz, /nl/quiz — prerendered per-locale routes with correct
  canonical + hreflang (new optional `path` prop on Base.astro).
- Progressive enhancement: the twelve questions and the full scoring key
  (bands + per-area guidance with deep links into the guide) are
  server-rendered and readable with JavaScript disabled; the client script
  only computes the live score and reveals the result panel.
- CSP-clean: bundled same-origin script (no inline handlers), bar widths
  set via a CSS custom property through the CSSOM (no inline styles), no
  third-party request. docker/csp.conf needs no new hash.
- i18n via the existing core+overlay model: src/data/quiz.json (neutral
  scoring) + src/i18n/content/<locale>/quiz.json (prose), loaded by a
  dedicated loadQuiz() that checks question/option/band parity in all three
  locales. Page chrome added to the `quiz` namespace (key parity tested).
- Share is copy-link + native Web Share + X (already allowlisted); the
  third-party mastodonshare.com redirector from PR #7 is dropped.
- TopBar "Contents" link made absolute (/#toc) so it works off the guide,
  plus a new "Quiz" nav link. New tests/e2e/quiz.spec.ts covers no-JS
  readability, scoring, the TOC link and zero third-party requests.

Co-Authored-By: arnaudom <1535627+arnaudom@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -11,8 +11,9 @@ In July 2026, the European Parliament let the "Chat Control" machinery advance
 Its promises, all enforced by tests:
 
 - **Static and self-contained** — no tracker, no cookie, not a single request to a third-party domain.
-- **Readable with JavaScript disabled** (Tor Browser "safest" mode included) — scripts only power the theme, filters and checklist.
+- **Readable with JavaScript disabled** (Tor Browser "safest" mode included) — scripts only power the theme, filters, checklist and quiz.
 - **Multilingual by design** — every language is a real prerendered route with correct `hreflang`; adding one means adding translation files, not touching code.
+- **Educational quiz** — `/quiz` scores your censorship resistance on a 0–100 scale and points you at concrete fixes in the guide. Server-rendered questions and scoring key (readable with JS off); the score itself is computed locally in the browser, nothing sent or stored.
 - **Printable and mirrorable** — a single-file offline version ships with every build.
 
 ## Stack