feat(a11y): adopt mod-blocks v2.4.0 so blocks carry heading levels

exampleSite/content/en/blocks-demo.md

@@ -0,0 +1,39 @@
+---
+title: Blocks Demo
+description: A single page that carries both content blocks and regular page content.
+showComments: false
+content_blocks:
+  - _bookshop_name: heading
+    heading:
+      title: A block on a page with content
+      content: >-
+        Blocks render above the page header, so on a page that also carries
+        content their titles are subsections and the page title below them
+        remains the only h1.
+  - _bookshop_name: cards
+    heading:
+      title: What the blocks look like
+    cols: 2
+    elements:
+      - title: Level from the page
+        icon: fas layer-group
+        content: >-
+          A page template hands its blocks a heading level. A list page renders
+          no header, so its first titled block opens the page. This page renders
+          a header, so its blocks start one level down.
+      - title: Level from the block
+        icon: fas sliders
+        content: >-
+          A block can set `heading_level` itself to pin a level, or `0` to keep
+          the plain division it rendered before heading levels existed.
+---
+
+## Regular page content
+
+Everything above this heading comes from `content_blocks` in the front matter.
+Everything from here down is ordinary Markdown, rendered through the page
+header and body.
+
+The page title is the `h1`. The two block titles above are `h2`, and this
+heading is an `h2` as well, so the page carries exactly one `h1` and skips no
+levels.

exampleSite/go.mod

@@ -5,11 +5,11 @@ go 1.19
 require (
 	github.com/FortAwesome/Font-Awesome v0.0.0-20260715180930-14c65a3747d0 // indirect
 	github.com/cloudcannon/bookshop/hugo/v3 v3.19.0 // indirect
-	github.com/gethinode/mod-blocks/v2 v2.3.6 // indirect
+	github.com/gethinode/mod-blocks/v2 v2.4.0 // indirect
 	github.com/gethinode/mod-bootstrap-icons/v2 v2.0.2 // indirect
 	github.com/gethinode/mod-cookieyes/v3 v3.1.0 // indirect
 	github.com/gethinode/mod-docs v1.15.7 // indirect
 	github.com/gethinode/mod-fontawesome/v6 v6.1.4 // indirect
-	github.com/gethinode/mod-utils/v6 v6.8.5 // indirect
+	github.com/gethinode/mod-utils/v6 v6.9.0 // indirect
 	github.com/twbs/icons v1.13.1 // indirect
 )

exampleSite/go.sum

@@ -4,6 +4,8 @@ github.com/cloudcannon/bookshop/hugo/v3 v3.19.0 h1:khb65FKbLXMWvm34OULEpKReCwNzE
 github.com/cloudcannon/bookshop/hugo/v3 v3.19.0/go.mod h1:s7mIonDhtsLcn10ZKuVXyqd6BDHI8vT1WQhZw8rPfY8=
 github.com/gethinode/mod-blocks/v2 v2.3.6 h1:xWvoWBfMXKTjsFuVh3sGZK80uQF1gl6gGt8w4GsZHiE=
 github.com/gethinode/mod-blocks/v2 v2.3.6/go.mod h1:/IfHiD5PCitH3IrpeMF/Pse/N+AbxkP8AYyIja8oJzk=
+github.com/gethinode/mod-blocks/v2 v2.4.0 h1:LjgEpU314lUPMpq63B/rWTUBzWTKTHDk1QSpPpADGJc=
+github.com/gethinode/mod-blocks/v2 v2.4.0/go.mod h1:bgbPL/PJzDFyvLcx7bd5uVJkkBDqFd0wZvA4DqqIdXs=
 github.com/gethinode/mod-bootstrap-icons/v2 v2.0.2 h1:KTQBwRB/1zRO3aS61bH2NNl/uTzelDLFxDjWbrqVKFc=
 github.com/gethinode/mod-bootstrap-icons/v2 v2.0.2/go.mod h1:oWYYQyAQgOFwrWwBZ8V+ztMCE7XmNTFbcmh28GWO2IA=
 github.com/gethinode/mod-cookieyes/v3 v3.1.0 h1:wan8yGs1bmwrgdySWSCqDbkiAsbTn8nWogwI+qKH6Is=
@@ -14,5 +16,7 @@ github.com/gethinode/mod-fontawesome/v6 v6.1.4 h1:6ppascnfF0Fy9csHLp2iVZVYhaguOO
 github.com/gethinode/mod-fontawesome/v6 v6.1.4/go.mod h1:VOzKLFEqI4O13IFZrKXOXFFHs26o8PgQtdv9fYUaxqA=
 github.com/gethinode/mod-utils/v6 v6.8.5 h1:hzJgNjw6NIORMvxeJ3Q6+qPaPzLc4CQtNTWRXFVjFPM=
 github.com/gethinode/mod-utils/v6 v6.8.5/go.mod h1:E5tO9w3VKaidJpu1nI8zAKmh0bddFHOIIQnudAaXQTs=
+github.com/gethinode/mod-utils/v6 v6.9.0 h1:+7RsNAfYCaM3rAzwrkTC6Ui3vcpGYWj1Ek1CmUVcaq0=
+github.com/gethinode/mod-utils/v6 v6.9.0/go.mod h1:E5tO9w3VKaidJpu1nI8zAKmh0bddFHOIIQnudAaXQTs=
 github.com/twbs/icons v1.13.1 h1:6bmNXvoeIbvjFWjfbjXg5JGbelLD1haIsMaEIzE9UZI=
 github.com/twbs/icons v1.13.1/go.mod h1:GnRlymgVWp5iVJCMa0Me5b6tFyGpVc2bSxPMRGIJmyA=