docs: fix changelog page heading levels and sidebar

Give the changelog page its own title so version headings become
sections: the current version now appears in the page ToC at the same
level as older versions. Fold the changelog link into the Development
sidebar section and use :titlesonly: to keep version headings out of
the sidebar. Exclude docs/changelog.rst from docstrfmt, which rewrote
the title to the same level as the included CHANGELOG.rst headings.

Assisted-by: ClaudeCode:claude-fable-5
Claude-Session: https://claude.ai/code/session_018JS2hRNjfymjCZez1jvGVV

Author: henryiii

.pre-commit-config.yaml

@@ -44,6 +44,8 @@ repos:
       - id: docstrfmt
         args: ["-l", "120"]
         additional_dependencies: ["sphinx>=9.1"]
+        # title must outrank the included CHANGELOG.rst headings
+        exclude: ^docs/changelog\.rst$
   - repo: https://github.com/astral-sh/ruff-pre-commit
     rev: aab412d509121cb5f7533134b7e67f9fab59c682 # frozen: v0.16.4
     hooks:

docs/changelog.rst

@@ -1 +1,5 @@
+===========
+ Changelog
+===========
+
 .. include:: ../CHANGELOG.rst