Adds an ordered chapter layer to series. Reading order becomes
(series_chapter.chapter_number, series_page.page_number); a chapter may be a
placeholder reserving a slot, and carries an optional parsed stated-page range
used to flag missing-page gaps. An image still lives in at most one series ⇒ one
chapter (image_id stays UNIQUE).
- models: series_chapter; series_page gains chapter_id (NOT NULL, cascade) +
stated_page. Migration 0040 backfills every existing series into one
auto-chapter holding its current flat pages — no data loss.
- SeriesService: chapter CRUD (create/update/reorder/delete/merge), page→chapter
assignment, reorder_pages, chapter-aware set_cover; list_pages now returns
chapters[] + gaps[] alongside a back-compat flat pages[]. Legacy series-wide
reorder operates on the single default chapter and rejects multi-chapter series.
- API: chapter endpoints under /api/series/<tag>/chapters; POST pages accepts an
optional chapter_id.
- TagService.merge now repoints series_chapter too, so a merged series' chapters
(and their pages) survive the source tag's deletion instead of cascading away.
- Tests: new chapter suite; updated the 4 direct SeriesPage(...) constructions to
supply chapter_id.
Frontend (chapter-aware manage view + reader) lands next; until then the
existing UI keeps working via the flat pages[] + single default chapter.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
bvandeusen