Upgrade the Pagefind version to v1.4.0

This version most notably sports an optional Playground (see
https://pagefind.app/docs/playground/) that _should_ help optimize the
search parameters better.

Release notes: https://github.com/Pagefind/pagefind/releases/tag/v1.4.0

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

hugo.yml

@@ -32,7 +32,7 @@ module:
     target: content
 params:
   hugo_version: 0.148.2
-  pagefind_version: 1.3.0
+  pagefind_version: 1.4.0
   latest_version: 2.51.0
   latest_relnote_url: https://raw.github.com/git/git/master/Documentation/RelNotes/2.51.0.adoc
   latest_release_date: '2025-08-18'