Refactor ChangeSet page update to rebuild entire page atomically
    
    Changes update_changeset_page to rebuild the entire ChangeSet wiki page
    with both System-Wide and Self-Contained changes sections in a single
    operation, rather than updating sections individually. This ensures
    both sections are always in sync and prevents partial updates.
    
    Key changes:
    - update_changeset_page now takes both systemwide and selfcontained content
    - Extracts page header and rebuilds complete page structure
    - update_all_changesets generates both change types before page update
    - Improved logging with change counts for both sections
    
    🤖 Generated with [Claude Code](https://claude.com/claude-code)
    
    Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>