feat(hg): revset-based author query, group discovery, one-shot ingest script

Rewrites the hg worker to use json-log?rev=author() which matches the
changeset author (not the pusher), capturing commits landed by sheriffs.
Repos are discovered within configured groups plus individually listed
repos. The worker skips entirely after the first successful backfill.

Adds script/hg-ingest.sh for offline ingestion via local hg clones —
clones one repo at a time, caches extracted changesets to .tsv, inserts
via psql, and sets poller_state when done.

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

asset/config/worker.env.tmpl

@@ -14,8 +14,9 @@ GITEA_TOKEN={{GITEA_TOKEN}}
 GITEA_POLL_INTERVAL_SECS=600
 
 HG_HOST=hg-edge.mozilla.org
-HG_REPOS=build/puppet,build/tools,build/buildbot-configs
-HG_AUTHOR_TERMS=thijssen,grenade
+HG_GROUPS=build,integration
+HG_REPOS=mozilla-central
+HG_AUTHOR_TERMS=rthijssen,grenade
 HG_POLL_INTERVAL_SECS=86400
 
 BUGZILLA_HOST=bugzilla.mozilla.org