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/adapters/mangadex.js

@@ -3,6 +3,7 @@
 const API = 'https://api.mangadex.org';
 const { parse } = require('../plugins/registry');
 const { localizedTitle, chapterNumber, selectChapterReleases, availabilitySummary, pageUrls } = require('../plugins/mangadex');
+const { sourceDate } = require('../../chapter-dates');
 
 function mangaDexInfo(value) {
   let url;
@@ -71,8 +72,9 @@ async function discoverMangaDexChapter(ref, http) {
   const atHome = await jsonGet(http, `${API}/at-home/server/${ref.id}?forcePort443=true`);
   const groupName = ref.group?.name ? ` · ${ref.group.name}` : '';
   const parsed = parse('mangadex', 'atHome', { data: { response: atHome, chapterUrl: ref.url, expectedPages: ref.pages }, url: `${API}/at-home/server/${ref.id}` });
+  const source = sourceDate(ref.uploadedAt, `MangaDex${groupName}`, ref.uploadBatch);
   return {
-    number: ref.number, title: ref.title || '', added: ref.added,
+    number: ref.number, title: ref.title || '', ...(source ? { dates: { source } } : {}),
     ...(ref.special ? { special: true, label: ref.label, sourceId: ref.id, sourceNumber: ref.sourceNumber ?? null } : {}),
     source: { name: `MangaDex${groupName}`, url: ref.url },
     pages: parsed.pages,