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/scraper-service.md

@@ -32,7 +32,7 @@ npm run start:scraper   # daemon only
 ```
 
 These commands are for native development only. The current Windows installation
-runs the three-service Docker Compose stack; the old Scheduled Task is disabled.
+runs the Docker Compose stack; the old Scheduled Task is disabled.
 Never start a native supervisor or daemon against its mounted state. Its observed
 ports, logs, persisted settings, restart procedure, and recovery snapshot are recorded in
 [`local-deployment.md`](local-deployment.md).