Serves contribution events from pipeline.db. Classifies PRs as
create/enrich/challenge, normalizes contributors, derives summaries
from branch names when descriptions are empty. Hot sort uses
challenge*3 + enrich*2 + signal / hours^1.5 decay from event time.
Domain and contributor filters, pagination (limit/offset).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
