Store: Smashwords as a family-filtered book source; free audiobooks stream through the hub; extensions and Sites on Home

- Smashwords: free EPUBs from its shelf feed, filtered (adult/erotica flags, LGBTQ+, keywords, unlabelled romance); admin saves a Smashwords sign-in (encrypted) used to download
- LibriVox chapter audio is fetched and streamed by the hub (with seeking) instead of redirecting the browser to archive.org
- Home: a My apps section with installed extensions and Sites, also in the command palette

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

README.md

@@ -164,3 +164,7 @@ One **Store** tab (turn it on per person) with sections for **Books** (the free
 
 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.
 
+**Smashwords** is a book source in the Store (Books). It lists Smashwords' most downloaded free EPUBs through its own shelf feed, filtered for a family: anything Smashwords flags as adult or erotica, anything in LGBTQ+, anything whose categories, tags or description say so, and any romance that does not say it is clean (sweet, Christian, inspirational...). The filter is automatic and cannot be perfect, so a book can occasionally slip through. Smashwords has no public search, so searching looks through a remembered set of about 400 of its popular free books. Downloading needs a free Smashwords account: an admin enters it once under Books, *Catalogues* (kept encrypted on the server, used only to sign in at smashwords.com). `SMASHWORDS_LANG` (default `1`, English) picks the language.
+
+**My apps on Home:** the extensions a person installed from My Store, and any Sites in My Store, appear under *My apps* on Home and in the command palette.
+