Completes FC-6.1: the series management UI now works in chapters.
- SeriesManageView: chapters as cards (inline-rename, stated-page range inputs,
move up/down, merge-into-previous, delete, pick-as-add-target), pages
drag-reorder WITHIN a chapter, a "gap: N-M missing" badge between chapters
with a stated-page hole, and Add chapter / Add placeholder. The picker adds
the selection into the targeted chapter.
- seriesManage store: chapter CRUD + reorderChapters/moveChapter/mergeChapter/
reorderPages actions; consumes chapters[]/gaps[]; addSelected targets a chapter.
- Reader: page_number is now within-chapter, so anchors switched to a global
`seq` (reading-order position) — fixes scroll/jump/active collisions across
chapters — plus chapter-title dividers at each chapter boundary.
- Updated seriesManage.spec to the chaptered store shape.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
bvandeusen