My Store: Add many books, with title, author, description and cover read out of each EPUB

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

README.md

@@ -163,6 +163,7 @@ One **Store** tab (turn it on per person) with sections for **Books** (the free
 
 **My Store** is your own catalogue, for everyone who has the Store tab. The admin adds items with **Add**: upload files, or copy a file from their Seafile (**From Files**), with an optional cover picture.
 - **Books** (EPUB, PDF, MOBI, AZW3, DOCX): *Add to my library* puts a copy on that person's shelf, or download it.
+  - **Add many books** (admin): pick a whole batch of book files at once. Each one is uploaded on its own and the server reads the **title, author, description and cover picture out of the EPUB itself** (`epubmeta.js`, no libraries); a book already in the store (same file) is skipped. PDF, MOBI, AZW3 and DOCX carry little usable metadata, so they are named after the file, with no author or cover. When it finishes it lists any book with no cover or no author so you can fix those with *Edit*.
 - **Music** (MP3, M4A, AAC, FLAC, OGG, OPUS, WAV): an album can have many tracks; they play in the hub's player and can be downloaded.
 - **Apps**: any files to download (an APK, an installer...), with an optional link and version. The hub does not run them.
 - **Sites**: any website as a card. It opens in a new tab, or inside the hub if you tick *Open inside the hub* (some sites refuse to be shown that way).