docs: exclude blog/category from git-revision-date plugin to fix build warning

The auto-generated blog category pages triggered a git timestamp ordering
warning because they have no real git history. Excluding them matches the
existing blog/archive exclusion.

Co-authored-by: Ralphify <noreply@ralphify.co>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 3 people

mkdocs.yml

@@ -90,6 +90,7 @@ plugins:
       fallback_to_build_date: true
       exclude:
         - blog/archive/*
+        - blog/category/*
 
 extra_css:
   - stylesheets/extra.css