feat(authors): add Goodreads as an author metadata source

Audnexus was the only author provider, and it returns just an ASIN, name,
description and image. Goodreads carries a far richer author record, so add it
as a second provider and let each field choose where it comes from.

The Goodreads API was retired in 2020, so the provider scrapes: a name resolves
to an author id through the WAF-free /book/auto_complete endpoint, falling back
to the author search page for names that only differ by a middle initial, and
the author page yields the biography, photo, birth and death dates, website,
genres and influences. Two rendering quirks are worth knowing about, since both
silently return the wrong value: free-text fields appear twice, truncated and
whole, so the parser takes whichever copy carries the most content; and the
birthplace sits in a bare text node while only the date is wrapped in a
dataItem, so authors with a place but no date correctly store nothing.

Preferences are now per field, mirroring the book-side FieldPreference model,
with an ordered provider list and a merge strategy each. They are global,
because an author row is shared across every library and cannot hold a
different biography per library. Providers declare which fields they can return
and both the resolver and the settings UI filter on that, so Audnexus can never
be assigned to a field it has no way to fill. The single global write mode is
migrated into each field's merge strategy on first read, keeping an existing
install's overwrite behaviour instead of silently adopting the default.

The executor now queries every listed provider and resolves each field
independently, first non-empty value winning, and records which provider
supplied the record so a re-run can pin the match instead of searching by name
again. overwriteIfProvided skips empty values, which is what lets a matched
author with an empty Audnexus biography fall through to Goodreads.

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

@@ -1,8 +1,8 @@
 {
-  "totalRoutes": 374,
+  "totalRoutes": 376,
   "byPermission": {
     "(none)": 166,
-    "Permission.ManageMetadataConfig": 32,
+    "Permission.ManageMetadataConfig": 34,
     "Permission.EmailSend": 30,
     "Permission.LibraryEditMetadata": 33,
     "Permission.BookDockAccess": 16,