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>

server.js

@@ -1218,10 +1218,13 @@ if (FULL_SCAN_MINUTES > 0) setInterval(() => {
 
 // A completed scraper publish increments a durable revision. Polling it here keeps the
 // reader index fresh without exposing an unauthenticated rescan endpoint to the daemon.
-let scraperRevision = null;
+let scraperRevision = null, revisionRoute = true;
 async function pollScraper() {
   try {
-    const state = await scraperRequest('/api/state');
+    // /api/revision is a few bytes; the full state is ~100 KB and makes the scraper summarise the library.
+    let state;
+    if (revisionRoute) state = await scraperRequest('/api/revision').catch(error => { if (error.code !== 404) throw error; revisionRoute = false; });
+    if (!revisionRoute) state = await scraperRequest('/api/state'); // a scraper from before /api/revision
     const revision = Number(state.publishedRevision || 0);
     if (scraperRevision === null || revision > scraperRevision) {
       const checked = await refreshChanged();