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>

tools/check.js

@@ -4,9 +4,8 @@ const { secret } = require('../runtime/config');
 const token = secret('SCRAPER_TOKEN');
 const root = process.env.READER_URL || 'http://127.0.0.1:8080';
 const scraper = process.env.SCRAPER_URL || 'http://127.0.0.1:8091';
-const sentinel = process.env.SENTINEL_URL || 'http://127.0.0.1:8092';
 (async () => {
-  for (const [name, base, endpoint] of [['reader', root, '/health'], ['scraper', scraper, '/api/state'], ['sentinel', sentinel, '/api/state']]) {
+  for (const [name, base, endpoint] of [['reader', root, '/health'], ['scraper', scraper, '/api/state']]) {
     try {
       const response = await fetch(base + endpoint, { headers: token ? { authorization: `Bearer ${token}` } : {}, signal: AbortSignal.timeout(10000) });
       if (!response.ok) throw new Error(`HTTP ${response.status}`);