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/collections.md

@@ -65,7 +65,7 @@ membership edits. It should preserve rejected decisions and report uncertainty.
 It must not turn a shared-universe link into an automatic collection or an unquestioned
 reading order. No embedded LLM, API credentials, automatic research loop, or autonomous
 catalog approval is enabled in this release. That optional capability belongs behind
-this same evidence/review boundary, not inside adapters or Sentinel.
+this same evidence/review boundary, not inside adapters or the scraper's stall watchdog.
 
 ## Persistence and API contract