Site: search over the documentation (#60)

A search page whose index is the page itself: one item for each page and
each heading of the guide, the how-tos, the FAQ and the developer docs,
written by Zola from the pages' own content. A small script filters and
ranks them as you type. Nothing is fetched, so the Content-Security-Policy
needs nothing new; without JavaScript the page is a list of every heading.

The navigation gets a link, and the documentation's index pages a box that
is a plain form to /search/?q=. The devlog is not searched.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

site/templates/base.html

@@ -33,6 +33,7 @@
     <a href="/dev/">Developers</a>
     <a href="/downloads/">Downloads</a>
     <a href="/devlog/">Devlog</a>
+    <a href="/search/">Search</a>
     <button class="link-btn js-only" id="theme-toggle" type="button">Light</button>
     <a class="btn btn-primary n-md" href="{{ config.extra.repo }}">Source</a>
   </nav>