fix: batch and index the crawler_jobs retention reaper

reap_terminal was one unbatched DELETE with no updated_at index — a full scan and
long-held lock over a large backlog (audit M5). Migration 0040 adds a partial
index on (updated_at) WHERE state IN ('done','dead'); reap_terminal now deletes in
bounded 5k batches. Existing tests green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.128.19",
+  "version": "0.128.20",
   "private": true,
   "type": "module",
   "scripts": {