Add authors pages and requestType notifications

Introduce full authors browsing/detail feature and enhance notifications to support type-specific titles.

- Add server APIs: authors search, author detail, and author books routes (audnexus integration) that require auth and enrich results with library matches.
- Add frontend pages/components: /authors listing and /authors/[asin] detail pages; AuthorCard, AuthorGrid, AuthorDetailCard, SimilarAuthorsRow, and related skeletons.
- Add hook and integration stubs: new useAuthors hook and audnexus-authors integration; update audible service to expose audibleBaseUrl.
- Update AudiobookDetailsModal to use audibleBaseUrl and link author names to author detail pages.
- Add header navigation link to Authors.
- Notifications: extend docs and code to include requestType (audiobook|ebook), add getEventTitle/getEventMeta helpers, update queue signature and providers/processors/tests to pass/handle requestType so titles can be resolved per request type.
- Misc: job queue, processors, provider tests and notification tests updated to reflect new behavior.

This change enables browsing authors and provides type-aware notification titles without per-provider changes.

src/lib/processors/send-notification.processor.ts

@@ -18,7 +18,7 @@ export type { SendNotificationPayload } from '../services/job-queue.service';
  * Calls NotificationService to send notifications to all enabled backends
  */
 export async function processSendNotification(payload: SendNotificationPayload): Promise<void> {
-  const { event, requestId, issueId, title, author, userName, message, jobId } = payload;
+  const { event, requestId, issueId, title, author, userName, message, requestType, jobId } = payload;
 
   const logger = RMABLogger.forJob(jobId, 'SendNotification');
 
@@ -34,6 +34,7 @@ export async function processSendNotification(payload: SendNotificationPayload):
       author,
       userName,
       message,
+      requestType,
       timestamp: new Date(),
     });