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>

package.json

@@ -9,11 +9,10 @@
     "start:scraper": "node scraper/daemon.js",
     "start:peer": "node peering/gateway.js",
     "start:all": "node tools/start-all.js",
-    "start:sentinel": "node sentinel/daemon.js",
     "check": "node tools/check.js",
     "check:compose": "node tools/compose-control.js check",
-    "test:runtime": "node --test sentinel/test/*.test.js",
-    "test:compose": "node tools/test-compose.js",
+    "test:runtime": "node --test runtime/test/*.test.js",
+    "test:compose":"node tools/test-compose.js",
     "test:ui": "node tools/test-compose.js --settings-ui --queue-ui --collections-ui --reading-ui",
     "test:direction-ui": "node tools/test-compose.js --direction-ui",
     "test:discovery-ui": "node tools/test-compose.js --discovery-ui",