Books: book store with Project Gutenberg, Standard Ebooks, Internet Archive and OPDS catalogues

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UaC9HmtHMdRP8dAbN4wAKj

README.md

@@ -59,6 +59,7 @@ e.g. hub.necloud.us. Settings: `SEAFILE_URL`, `ONLYOFFICE_URL` env vars in docke
 - **Books**: an e-book reader for **EPUB, PDF, DOCX, MOBI, AZW and AZW3** (Media group; give it to people in Settings -> People as *Books*). Add files with the button or by dropping them on the page (up to 300 MB each; the server checks a file really is what its name says and does not store the same book twice). Titles, authors and covers are read out of the books in the browser; long-press or right-click a book to edit, download or delete it. Each person has their own shelf in `/data/users/<id>/books/`.
   - **Reading**: EPUB uses epub.js (pages or scroll, two-page spreads on wide screens), PDF uses pdf.js (continuous scroll, zoom, selectable text, dark and sepia tints) DOCX is converted to HTML by mammoth, and MOBI, AZW and AZW3 are read by `@lingo-reader/mobi-parser`; both are shown in a frame that cannot run scripts (scroll only, with contents from the book or its headings). Contents, search inside the book, a progress slider, tap the edges or use the arrow keys, swipe on touch screens, tap the middle to hide the bars. Appearance (theme, text size, font, line spacing, margins, layout, zoom) is remembered on each device.
   - **Synced**: where you got to, bookmarks, highlights (four colours) and notes are kept on the server, so a book opens where you left off on any device; two devices adding notes at once keep both (the newest edit of the same note wins). Continue reading on the library page, sorting and search, and *Copy as text* exports a book's notes.
+  - **Book store** (Books -> Book store): search free, DRM-free books from **Project Gutenberg** (through Gutendex), **Standard Ebooks**, the **Internet Archive** (public-domain EPUBs only; borrow-only items are refused) and any **OPDS catalogue** an admin adds under *Catalogues* (Calibre-Web, Kavita, Komga and so on; an optional username and password are kept encrypted on the server and never sent to the browser). One search covers every source, results show their cover and source, and *Add to library* downloads the book on the server straight onto your shelf. The server only ever contacts a source's own addresses (redirects to other sites are refused), covers come through the hub, and a catalogue book must live on that catalogue's own address. Settings: `GUTENDEX_URL`, `STANDARD_EBOOKS_URL` and `ARCHIVE_URL` can point at mirrors. `node tools/store-test.js` tests it against fake catalogues; it has not been run against the live sites from the build environment, so if one of them changes its feed format, the line under the search box names the source that failed.
   - The reader scripts are in `public/vendor/reader/` (epub.js, JSZip, pdf.js, mammoth, the MOBI parser) and load only when a book is opened or added. `node tools/books-test.js` tests the server; `python3 tools/mkbooks.py <dir>` makes a small EPUB, PDF and MOBI to try. **DRM-protected books are refused** (a Kindle file with copy protection is detected on upload and the reason is shown); only DRM-free books work. The MOBI reader was tried on a generated MOBI 6 file, not on real Kindle files, so tell me about any book that opens oddly. Not included: text-to-speech, offline reading.
 - **Signal**: your Signal chats inside the app, **on desktop-class screens only** (a window at least 900 px wide with a mouse or trackpad; phones and touch tablets don't
   see it). Besides the Signal tab there is a chat button on **every** screen that opens a panel over whatever you are doing (close it with the x; the