- parsePDF: return all text as single 'Full Text' chapter (admin splits manually)
- parseEPUB: fix chapter numbering to use sequential counter not spine index
- Remove dead code: chaptersFromBookmarks, cleanChapterText, extractChaptersFromText, chapterHeadingRE; drop pdfcpu alias and regexp imports
- Backend: POST /api/admin/books/:slug/split-chapters endpoint — splits text on '---' dividers, optional '## Title' headers, writes chapters via WriteChapter
- UI: admin panel now shows for all admin users regardless of source_url; chapter split tool shown when book has single 'Full Text' chapter, pre-fills from MinIO content