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>

public/health.js

@@ -13,8 +13,7 @@
       backup.draw(health.backup);
       main.textContent = '';
       main.append(h('section', { class: 'card' },
-        h('p', {}, `Reader: ${health.reader.ok ? 'healthy' : 'scan error'} · Sentinel: ${health.sentinel.status} · Scraper: ${scraper.status || 'unavailable'}`),
-        h('p', { class: 'muted small' }, health.sentinel.checkedAt ? `Last independent check: ${new Date(health.sentinel.checkedAt).toLocaleString()}` : 'Sentinel has not reported yet.'),
+        h('p', {}, `Reader: ${health.reader.ok ? 'healthy' : 'scan error'} · Scraper: ${scraper.status || 'unreachable'}`),
         h('a', { class: 'btn', href: 'settings.html#admin/scraper' }, 'Queue & hoster settings')));
       for (const entry of scraper.active || []) main.append(h('section', { class: 'card' }, h('h2', {}, entry.source),
         h('p', {}, `${entry.current.title} · ${entry.job?.completed || 0}/${entry.job?.total || '?'} chapters`),
@@ -27,7 +26,7 @@
           if (item.failure?.kind === 'access' && !confirm('Has the source access problem been resolved? This manually authorizes one retry.')) return;
           await api('api/admin/scraper', { command: 'control', action: item.status === 'unavailable' ? 'inspect' : 'retry', id: item.id }); load();
         } }, item.status === 'unavailable' ? 'Inspect source' : 'Retry'), h('button', { class: 'btn', onclick: async () => { await api('api/admin/scraper', { command: 'control', action: 'skip', id: item.id }); load(); } }, 'Skip job')))) : h('p', { class: 'muted' }, 'No failed jobs.')));
-      const incidents = [...(health.sentinel.incidents || []), ...(scraper.incidents || [])];
+      const incidents = scraper.incidents || [];
       main.append(h('details', { class: 'card', open: incidents.some(i => i.state === 'open') }, h('summary', {}, 'Incident & recovery history'), incidents.slice(-50).map(i =>
         h('p', {}, `${i.at} · ${i.state} · ${i.message || i.failure?.message || ''}${i.resolution ? ' · ' + i.resolution : ''}`))));
     } catch (e) { main.textContent = ''; main.append(h('p', { class: 'error', role: 'alert' }, e.message)); }