Store: one tab combining books, free audiobooks and radio, plus My Store for your own books, music, apps and sandboxed extensions

- Store tab with sections; the book store, LibriVox and radio finder are shown inside it (old entry points redirect)
- My Store: admin uploads files or copies from Seafile; books go to a person's shelf, music plays in the player, apps download
- Extensions: one HTML file run in a sandboxed frame with a small storage/toast/user bridge; example in docs/extensions

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

README.md

@@ -150,3 +150,16 @@ playing an episode or pressing the button still works. Settings -> Health shows
 - **Search what's said** (Podcast screen): finds a word or phrase in every transcript on the server and plays that episode from that moment. Only podcasts on your own list (and audiobooks) are searched; older transcripts are matched to their episode the first time.
 - **Recipes** (needs `MEALIE_TOKEN`; `MEALIE_URL` defaults to `https://mealie.necloud.us`): browse and search your Mealie recipes, read one (ingredients, steps, times), import a recipe from a web link, and add its ingredients to the Mealie shopping list (Mealie adds up repeats). The shopping list is also kept in **Tasks** as a "Shopping" list: ticking, adding or deleting an item in either place is carried over when either screen opens or an item changes. Turn the tab on per person in the admin screen.
 - **Contacts**: an address book per person (name, company, emails, phones, address, birthday, notes). Mail suggests contacts while you type a recipient, a message you are reading can be saved as a contact (or opens the one you have), birthdays appear in the Calendar, and .vcf files from iCloud, Google or a phone can be imported and exported.
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+## Store
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+One **Store** tab (turn it on per person) with sections for **Books** (the free book sources, Open Library and any OPDS catalogue), **Audiobooks** (LibriVox) and **Radio** (the station finder), each shown only to people who have that tab, plus **My Store**. The old Book store and Free audiobooks buttons now open the Store.
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+**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.
+- **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.
+- **Extensions**: one self-contained `.html` file that adds a feature to the hub. A person installs it from My Store and it opens inside the Store. It runs in a sandbox with no access to the hub's sign-in or data (and `connect-src https:` only), and talks to the hub through a small `hub` object: `hub.storage.get/set/all/remove` (its own settings for that person, up to 256 KB), `hub.user()` (the person's name), `hub.toast(text)` and `hub.open(url)`. See `docs/extensions/notepad.html` for a complete example.
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+Files are kept in the data folder under `mystore/` (up to 1 GB each; extensions up to 2 MB). Only an admin can add, change or delete items.
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