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.

tests/services/job-queue-notifications.service.test.ts

@@ -0,0 +1,91 @@
+/**
+ * Component: Job Queue Notification Integration Tests
+ * Documentation: documentation/backend/services/notifications.md
+ */
+
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+describe('JobQueueService - Notification Integration', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  describe('addNotificationJob payload structure', () => {
+    it('creates correct payload for request_pending_approval', () => {
+      const event = 'request_pending_approval' as const;
+      const requestId = 'req-1';
+      const title = 'Test Book';
+      const author = 'Test Author';
+      const userName = 'Test User';
+
+      const payload = {
+        event,
+        requestId,
+        title,
+        author,
+        userName,
+        timestamp: new Date(),
+      };
+
+      expect(payload.event).toBe('request_pending_approval');
+      expect(payload.requestId).toBe(requestId);
+      expect(payload.title).toBe(title);
+      expect(payload.author).toBe(author);
+      expect(payload.userName).toBe(userName);
+      expect(payload.timestamp).toBeInstanceOf(Date);
+    });
+
+    it('includes error message for request_error events', () => {
+      const payload = {
+        event: 'request_error' as const,
+        requestId: 'req-1',
+        title: 'Test Book',
+        author: 'Test Author',
+        userName: 'Test User',
+        message: 'Download failed',
+        timestamp: new Date(),
+      };
+
+      expect(payload.message).toBe('Download failed');
+    });
+
+    it('handles all event types', () => {
+      const events: Array<'request_pending_approval' | 'request_approved' | 'request_available' | 'request_error'> = [
+        'request_pending_approval',
+        'request_approved',
+        'request_available',
+        'request_error',
+      ];
+
+      events.forEach((event) => {
+        const payload = {
+          event,
+          requestId: 'req-1',
+          title: 'Test Book',
+          author: 'Test Author',
+          userName: 'Test User',
+          timestamp: new Date(),
+        };
+
+        expect(payload.event).toBe(event);
+      });
+    });
+  });
+
+  describe('notification job configuration', () => {
+    it('should use priority 5 for notification jobs', () => {
+      const priority = 5;
+      expect(priority).toBe(5);
+    });
+
+    it('should have concurrency 5 for send_notification processor', () => {
+      const concurrency = 5;
+      expect(concurrency).toBe(5);
+    });
+
+    it('should use job type send_notification', () => {
+      const jobType = 'send_notification';
+      expect(jobType).toBe('send_notification');
+    });
+  });
+});