Move schema changelog to bottom of docs page (#206)

The schema.description field contains the revision-history changelog
rather than a conceptual intro, so rendering it at the top of the
page was making the docs feel dense and dated. Move it into a
collapsed "Revision history" callout at the bottom of the page.
The hand-written "How this schema is organized" section now leads.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: rdhyee

tools/docgen/index.qmd.jinja2

@@ -4,8 +4,6 @@ subtitle: Schema documentation generated from linkml sources.
 date-modified: {{ gen.timestamp }}
 ---
 
-{{ schema.description }}
-
 URI: {{ schema.id }}
 Name: {{ schema.name }}
 
@@ -126,3 +124,11 @@ No enumerations are defined.
 {% else %}
 No subsets are defined.
 {% endif %}
+
+## Revision history
+
+::: {.callout-note collapse="true"}
+## Schema changelog
+
+{{ schema.description }}
+:::