Chapter dates: read date setting and tiered release dates (BL-0047)

- Chapter rows show when you first finished a chapter (setting: date + hour,
  date, off) from a new durable progress doneAt; older reads fall back to the
  reading clock's earliest remembered completion.
- chapter.json keeps added (arrival in this library, now kept on replace) plus
  x-dates.source (source upload, bulk imports flagged), x-dates.release
  (official, for a later metadata job) and x-dates.ecosystem (first entry into
  any Manga Circus library; carried over peering, earliest wins, clamped).
- Rows show one release date by tier: official > source upload > ecosystem >
  library, with all known dates in the tooltip (setting to hide).
- Fixes: WeebCentral dates came from the chapter page, which has none (every
  chapter got the download time); they now come from the full chapter list.
  MangaDex no longer writes a group's publishAt into added. Peering sends dates.
- tools/backfill-chapter-dates.js migrates an existing library (dry run default).
- Coverage dry run on the server: docs/chapter-dates-coverage-2026-10-24.md.

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

scraper/plugins/mangadex.js

@@ -1,6 +1,7 @@
 'use strict';
 
 const { specialKey } = require('../../chapter-identity');
+const { batchFlags } = require('../../chapter-dates');
 
 function localizedTitle(attributes = {}) {
   const titles = attributes.title || {};
@@ -41,14 +42,18 @@ function selectChapterReleases(resources = [], specialLabel = 'Special') {
     const prior = selected.get(number);
     if (!prior || compareRank(resource, prior) < 0) selected.set(number, resource);
   }
-  return [...selected.entries()].map(([number, resource]) => {
+  const chosen = [...selected.entries()];
+  const uploaded = chosen.map(([, resource]) => resource.attributes?.publishAt || resource.attributes?.readableAt || resource.attributes?.createdAt);
+  const batches = batchFlags(uploaded);
+  return chosen.map(([number, resource], index) => {
     const group = groupFor(resource);
     return {
       id: resource.id, number, title: resource.attributes?.title || '',
       ...(!chapterNumber(resource.attributes?.chapter) ? { special: true, label: specialLabel, sourceId: resource.id, sourceNumber: resource.attributes?.chapter ?? null } : {}),
       ...(resource.attributes?.volume ? { volume: chapterNumber(resource.attributes.volume) || String(resource.attributes.volume) } : {}),
       pages: Number(resource.attributes?.pages || 0),
-      added: resource.attributes?.publishAt || resource.attributes?.readableAt || resource.attributes?.createdAt,
+      // A group's upload time, not an official release; bulk uploads are flagged.
+      ...(uploaded[index] ? { uploadedAt: uploaded[index], uploadBatch: !!batches[index] } : {}),
       group,
       url: `https://mangadex.org/chapter/${resource.id}`,
     };