Support language/format/publisher for Audible

Expose language, formatType, and publisherName from the Audible catalog. Update audible.service to map format_type and publisher_name (and language) into the AudibleAudiobook model, update AudiobookDetailsModal to display language and format using the CSS "capitalize" class, and update documentation to list the new fields. Add unit tests to verify the mappings, details propagation, and behavior when fields are omitted.

documentation/integrations/audible.md

@@ -250,6 +250,9 @@ interface AudibleAudiobook {
   series?: string;
   seriesPart?: string;
   seriesAsin?: string;
+  language?: string;
+  formatType?: string;
+  publisherName?: string;
 }
 
 interface EnrichedAudibleAudiobook extends AudibleAudiobook {