Read-ahead per reader; compose passes READ_AHEAD and PERF_TRACE; report fixes

Each user gets an own read-ahead queue, served in turn, so two people reading
at once no longer cancel each other's chapter. The report rounds phase times
and measures the quiet time before a slow storage probe correctly.

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

server.js

@@ -448,14 +448,14 @@ function continueOf(m, prog, s) {
   return next ? { c: next.id, text: 'Read next · ' + next.label } : { c: last.ch.id, v: last.p.v, text: 'Read again · ' + last.ch.label };
 }
 // From the saved page on, then the pages before it; afterwards the next chapter's preferred version.
-function warmChapter(m, ch, v, progress, s) {
+function warmChapter(u, m, ch, v, progress, s) {
   const from = Math.min(Math.max(0, +(progress && progress.v === v.id && progress.p) || 0), v.pages.length);
   const pages = v.pages.slice(from).concat(v.pages.slice(0, from)).map(p => path.join(LIB, v.rel, p.f));
-  readAhead.warm(pages, `${m.id}/${ch.id}`);
+  readAhead.warm(pages, `${m.id}/${ch.id}`, u.name);
   const next = neighbour(m, ch, 1, s), nextCh = next && m.chapterById.get(next.id);
   if (nextCh) {
     const nv = ranked(m, nextCh)[0].v;
-    readAhead.then(nv.pages.map(p => path.join(LIB, nv.rel, p.f)), `${m.id}/${nextCh.id}`);
+    readAhead.then(nv.pages.map(p => path.join(LIB, nv.rel, p.f)), `${m.id}/${nextCh.id}`, u.name);
   }
 }
 function neighbour(m, ch, step, s) {
@@ -768,7 +768,7 @@ const routes = {
     let seen = false;
     for (const n of db.notes[u.name] || []) if (!n.read && n.m === m.id && n.c === ch.id) seen = n.read = true;
     if (seen) save();
-    if (readAhead) warmChapter(m, ch, v, prog[ch.id], s);
+    if (readAhead) warmChapter(u, m, ch, v, prog[ch.id], s);
     return {
       perf: tracer.on,
       manga: { id: m.id, title: m.title },