fix(ui): derive Library Type dropdowns from library_types — audiobooks was missing

The audiobook library type shipped backend-complete (LibraryTypeAudiobooks
constant, allowed extensions, MIME map, schema seed row, GET
/api/libraries/types) but neither create-library form offered it: the
admin Create Library modal and the setup wizard's add-library step both
hardcoded their <option> lists to the original three types
(ebooks/comics/manga), so an audiobook library could not be created from
the UI.

Both dropdowns now render from the same DB-backed library_types table
the create API resolves types against — a future type appears without
template edits (the exact drift the rendering-ownership rule warns
about):

- templates/utils.go: OrderedLibraryTypes pins the historical dropdown
  order (ebooks, comics, manga, audiobooks) and appends unknown future
  types by name; LibraryTypeDisplayName renders labels with a
  capitalize-the-name fallback for types added without a label
- templates/admin_library.templ: new LibraryTypeOptions fragment used
  by the modal's select; AdminLibrary takes the types list
- templates/setup.templ: Setup takes the types list, same fragment
- internal/router/helpers.go: libraryTypeOptionsFor fetches via
  LibraryService.GetLibraryTypes, falling back to the built-in type
  names on DB failure so the forms stay usable (CreateLibrary still
  resolves the name against the DB, so the fallback is never
  authoritative)
- internal/router/frontend.go, internal/router/setup.go: pass the list
  into the two pages

Tests:
- templates/utils_test.go: pure unit tests for ordering + labels
- cmd/server/tests/admin_library_page_test.go: SSR regression —
  /admin/library must offer all four library types, audiobooks exactly
  once (options come from the DB loop, not a hardcode)

templates/setup.templ

@@ -1,6 +1,8 @@
 package templates
 
-templ Setup() {
+import "bookhoard/internal/database"
+
+templ Setup(libraryTypes []database.LibraryTypes) {
 	<!DOCTYPE html>
 	<html lang="en">
 		<head>
@@ -211,9 +213,7 @@ templ Setup() {
 								x-model="newLibrary.type"
 								class="input mt-2"
 							>
-								<option value="ebooks">Ebooks</option>
-								<option value="comics">Comics</option>
-								<option value="manga">Manga</option>
+								@LibraryTypeOptions(libraryTypes)
 							</select>
 						</div>
 						<div>