Fold the sentinel into the scraper and drop the sentinel service (BL-0046)

The stall watchdog now runs inside the scraper (ScraperService.checkStalls,
every 30 s from the work loop): same rule as before, one checkpoint-safe
restart, quarantine on the second stall, missing checkpoint is no evidence,
and paused time no longer counts. Stalls are recorded as scraper incidents
(failure.kind 'stall'). The private /api/recovery endpoint is gone.

Dropped with the service: reader/scraper-unreachable incidents (supervisor
and Docker handle crashes; the health page shows "Scraper: unreachable"),
duplicate job-failure incidents and the unused /metrics endpoint.
The stack is now reader + scraper (+ optional peer-gateway).
The supervisor test moved to runtime/test (npm run test:runtime stays).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/greatest.md

@@ -29,6 +29,6 @@ Public catalog chapter counts are often absent; the UI says “Chapters unknown
 
 ## Deployment and QA
 
-The Docker image now copies `greatest/` as app code; no new Compose service, volume, port, secret, or migration is needed. Rebuild/recreate **reader only** to pick up catalog/UI changes. The scraper and sentinel do not need restarting. Existing `data/db.json` accepts the new `greatestRatings` object without migration.
+The Docker image now copies `greatest/` as app code; no new Compose service, volume, port, secret, or migration is needed. Rebuild/recreate **reader only** to pick up catalog/UI changes. The scraper does not need restarting. Existing `data/db.json` accepts the new `greatestRatings` object without migration.
 
 Run `npm run test:reader` for catalog/API tests and `node tools/test-greatest-ui.js` for disposable headless-browser QA. The UI fixture blocks remote covers and never contacts the scraper. Manual catalog edits should preserve stable IDs once anyone has voted; changing a title's ID strands its votes.