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/app/api/requests/route.ts

@@ -252,9 +252,35 @@ export async function POST(request: NextRequest) {
         },
       });
 
+      const jobQueue = getJobQueueService();
+
+      // Send notification based on approval status
+      if (initialStatus === 'awaiting_approval') {
+        // Request needs approval - send pending notification
+        await jobQueue.addNotificationJob(
+          'request_pending_approval',
+          newRequest.id,
+          audiobookRecord.title,
+          audiobookRecord.author,
+          newRequest.user.plexUsername || 'Unknown User'
+        ).catch((error) => {
+          logger.error('Failed to queue notification', { error: error instanceof Error ? error.message : String(error) });
+        });
+      } else {
+        // Request was auto-approved (either automatic or interactive search) - send approved notification
+        await jobQueue.addNotificationJob(
+          'request_approved',
+          newRequest.id,
+          audiobookRecord.title,
+          audiobookRecord.author,
+          newRequest.user.plexUsername || 'Unknown User'
+        ).catch((error) => {
+          logger.error('Failed to queue notification', { error: error instanceof Error ? error.message : String(error) });
+        });
+      }
+
       // Trigger search job only if not skipped and not awaiting approval
       if (shouldTriggerSearch) {
-        const jobQueue = getJobQueueService();
         await jobQueue.addSearchJob(newRequest.id, {
           id: audiobookRecord.id,
           title: audiobookRecord.title,