Add notification system with admin UI and backend

Introduces a full notification system with support for Discord and Pushover backends, event triggers, and message formatting. Adds backend services, processors, and API endpoints for managing notifications, as well as a new Notifications tab in the admin settings UI. Updates documentation, database schema, and tests to cover notification features and approval workflow improvements. Also changes project license from MIT to AGPL v3.

src/lib/processors/plex-recently-added.processor.ts

@@ -184,7 +184,14 @@ export async function processPlexRecentlyAddedCheck(payload: PlexRecentlyAddedPa
         status: { notIn: ['available', 'cancelled'] },
         deletedAt: null,
       },
-      include: { audiobook: true },
+      include: {
+        audiobook: true,
+        user: {
+          select: {
+            plexUsername: true,
+          },
+        },
+      },
       take: 100,
     });
 
@@ -237,6 +244,19 @@ export async function processPlexRecentlyAddedCheck(payload: PlexRecentlyAddedPa
               },
             });
 
+            // Send notification that audiobook is now available
+            const { getJobQueueService } = await import('../services/job-queue.service');
+            const jobQueue = getJobQueueService();
+            await jobQueue.addNotificationJob(
+              'request_available',
+              request.id,
+              audiobook.title,
+              audiobook.author,
+              request.user.plexUsername || 'Unknown User'
+            ).catch((error) => {
+              logger.error('Failed to queue notification', { error: error instanceof Error ? error.message : String(error) });
+            });
+
             matchedDownloads++;
 
             // Trigger metadata match for Audiobookshelf items (only for our downloaded requests)