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>

scraper/AGENT_RUNBOOK.md

@@ -22,7 +22,7 @@ Runtime recovery is documented in `../docs/resilience.md`. Request-level 5xx ret
 remain limited to 30/60 seconds; after those are exhausted the daemon can resume the
 same checkpoint once after a five-minute source cooldown. No automatic access-error
 retry is permitted. Unavailable titles and parser failures are job-scoped; repeated
-independent parser failures stop the source lane. Sentinel never changes adapters.
+independent parser failures stop the source lane. The stall watchdog never changes adapters.
 
 ```text
 public metadata -> cached series metadata