docs: enable site search via @antora/lunr-extension

[sgerbino]

Closes #401.

@antora/lunr-extension was already a dependency in doc/package.json but was never registered under antora.extensions in doc/local-playbook.yml, so the built site shipped no search. This registers it, first in the extension list with index_latest_only: true, matching the convention used by Boost.URL, dynamic_bitset, and openmethod.

Verified with a full local build_antora.sh run:

• search-index.js (2.8 MB) is generated at the site root
• _/js/vendor/lunr.js and _/js/search-ui.js are injected by the extension
• Pages render the toolbar search box and load all three scripts

No UI-bundle changes are needed: the Boost UI's toolbar.hbs and footer-scripts.hbs are gated on SITE_SEARCH_PROVIDER, which the extension sets at build time.

[cppalliance-bot]

An automated preview of the documentation is available at https://428.capy.prtest3.cppalliance.org/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2026-09-25 19:39:49 UTC

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.09%. Comparing base (ca59f94) to head (a29aa63).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #428   +/-   ##
========================================
  Coverage    98.09%   98.09%           
========================================
  Files          130      130           
  Lines         6289     6289           
========================================
  Hits          6169     6169           
  Misses         120      120           

Flag	Coverage Δ
linux	98.08% <ø> (ø)

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[cppalliance-bot]

GCOVR code coverage report https://428.capy.prtest3.cppalliance.org/gcovr/index.html
LCOV code coverage report https://428.capy.prtest3.cppalliance.org/genhtml/index.html
Coverage Diff Report https://428.capy.prtest3.cppalliance.org/diff-report/index.html

Build time: 2026-09-25 19:52:49 UTC