feat(books): remember a default read-aloud narration language

Resolve book languages stated as names ("English") to a code, so the
dialog and the server's fallback stop calling English unsupported. The
dialog groups the ebook and audiobook in a Sources card, shows
Highlighting without the Advanced disclosure, and saves a per-user
default under /user-preferences/read-aloud for books it cannot match.

server/test/e2e/authorization-matrix/route-inventory/manifest.json

@@ -1,7 +1,7 @@
 {
-  "totalRoutes": 677,
+  "totalRoutes": 679,
   "byPermission": {
-    "(none)": 287,
+    "(none)": 289,
     "Permission.ManageMetadataConfig": 41,
     "Permission.EmailSend": 34,
     "Permission.LibraryEditMetadata": 37,