Add stat panels for total created/deleted/updated challenges and a
full-width timeseries showing created vs deleted per period using
increase() over $__rate_interval.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Master

See merge request !1

# Conflicts:
#   .gitlab-ci.yml