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/services/job-queue.service.ts

@@ -155,6 +155,7 @@ export interface SendNotificationPayload extends JobPayload {
   author: string;
   userName: string;
   message?: string;
+  requestType?: string; // 'audiobook' | 'ebook' — drives type-specific notification titles
   timestamp: Date;
 }
 
@@ -948,7 +949,8 @@ export class JobQueueService {
     title: string,
     author: string,
     userName: string,
-    message?: string
+    message?: string,
+    requestType?: string
   ): Promise<string> {
     logger.info(`Queueing notification: ${event}`, { requestId, title, userName });
     return await this.addJob(
@@ -963,6 +965,7 @@ export class JobQueueService {
         author,
         userName,
         message,
+        requestType,
         // Pass the original ID for notification display (e.g., Discord footer)
         ...(event === 'issue_reported' && { issueId: requestId }),
         timestamp: new Date(),