Scraper: stop walking the whole library once a minute for status polls

The reader polled /api/state every 15 s; each call rebuilt the scraper's library
summary when it was over 60 s old, reading every chapter.json (on the NAS about
5,300 opens / 16,000 NFS calls and 1.3 s CPU per walk, once a minute, plus 115 KB
per poll). The reader now polls GET /api/revision (falls back to /api/state on an
older scraper), and the summary is rebuilt after a library change or after 15
minutes. Release-date writes invalidate it too.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scraper/daemon.js

@@ -35,6 +35,7 @@ async function body(req) {
       if (url.pathname === '/health') return json(res, 200, { ok: true, status: service.state.status });
       if (TOKEN && req.headers.authorization !== `Bearer ${TOKEN}`) return json(res, 401, { error: 'Unauthorized' });
       if (req.method === 'GET' && url.pathname === '/api/state') return json(res, 200, await service.publicState());
+      if (req.method === 'GET' && url.pathname === '/api/revision') return json(res, 200, service.revision());
       if (req.method !== 'POST') return json(res, 404, { error: 'Not found' });
       const input = await body(req);
       if (url.pathname === '/api/queue') return json(res, 200, { item: await service.enqueue(input), state: await service.publicState() });