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>

peering/test/peering.test.js

@@ -68,7 +68,8 @@ test('mTLS pairing, opt-in catalog, peer queue publication, and revocation', { t
   await fsp.mkdir(chapterDir, { recursive: true });
   await fsp.writeFile(path.join(mangaDir, 'manga.json'), JSON.stringify({ title: 'Sample Manga', direction: 'ltr' }));
   await fsp.writeFile(path.join(mangaDir, 'cover.png'), PNG);
-  await fsp.writeFile(path.join(chapterDir, 'chapter.json'), JSON.stringify({ title: 'The first chapter', source: { name: 'Local' } }));
+  await fsp.writeFile(path.join(chapterDir, 'chapter.json'), JSON.stringify({ title: 'The first chapter', source: { name: 'Local' },
+    added: '2026-10-01T08:00:00.000Z', 'x-dates': { version: 1, source: { at: '2026-09-30T15:00:00.000Z', name: 'WeebCentral', batch: false } } }));
   await fsp.writeFile(path.join(chapterDir, '0001.png'), PNG);
   const ga = await gateway(dataA, libA, portA, path.join(root, 'usage-a.json'));
   let gb = await gateway(dataB, libB, portB, path.join(root, 'usage-b.json'));
@@ -134,7 +135,13 @@ test('mTLS pairing, opt-in catalog, peer queue publication, and revocation', { t
   assert.equal(result.publishedCount, 1);
   assert.deepEqual(JSON.parse(await fsp.readFile(path.join(libB, 'Sample Manga', 'manga.json'), 'utf8'))['x-work-identity'], remote.workIdentity,
     'The stable work identity is stored with the imported peer edition');
-  assert.equal(fs.existsSync(path.join(libB, 'Sample Manga', 'v01', 'c0001 The first chapter [Peer ServerA ' + inB.id.slice(1, 7) + ']', '0001.png')), true);
+  const receivedDir = path.join(libB, 'Sample Manga', 'v01', 'c0001 The first chapter [Peer ServerA ' + inB.id.slice(1, 7) + ']');
+  assert.equal(fs.existsSync(path.join(receivedDir, '0001.png')), true);
+  const received = JSON.parse(await fsp.readFile(path.join(receivedDir, 'chapter.json'), 'utf8'));
+  assert.deepEqual(received['x-dates'].ecosystem, { at: '2026-10-01T08:00:00.000Z', via: 'peer ServerA' },
+    'The chapter keeps the date it first entered Manga Circus on A, not its arrival on B');
+  assert.equal(received['x-dates'].source.at, '2026-09-30T15:00:00.000Z');
+  assert.notEqual(received.added, '2026-10-01T08:00:00.000Z', '"added" is the arrival in B\'s own library');
   const second = await run(info, { scope: { mode: 'missing' }, existingPolicy: 'skip-any' },
     { libraryRoot: libB, settings: { chapterMinMs: 500 }, shouldStop: () => false });
   assert.equal(second.publishedCount, 0);