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>

.dockerignore

@@ -5,6 +5,7 @@
 !library.js
 !reading-direction.js
 !chapter-identity.js
+!chapter-dates.js
 !catalog.js
 !backup.js
 !reading-analytics.js