feat(search): 引入拼音搜索

* add pinyin search

* style(highlight): keep theme-aware background

- restore theme-aware .highlight with --highlight-bg

- add highlight vars for light/dark

chore: load pinyin lib before script.js

- ensure pinyin-match.js loads before script.js to avoid runtime dependency issues

docs: add third-party notice for pinyin-match

- add placeholder notice; replace with upstream license after verification

---------

Co-authored-by: neo <neo@example.com>
Co-authored-by: Maintainer (PR Edit) <maintainer@local>

templates/layouts/default.hbs

@@ -128,6 +128,7 @@
     <script id="menav-config-data" type="application/json" style="display: none;">
         {{{configJSON}}}
     </script>
+    <script src="pinyin-match.js"></script>
     <script src="script.js"></script>
 </body>
 </html>