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/api/requests-approval.routes.test.ts

@@ -13,6 +13,8 @@ const requireAdminMock = vi.hoisted(() => vi.fn());
 const prismaMock = createPrismaMock();
 const jobQueueMock = vi.hoisted(() => ({
   addSearchJob: vi.fn(),
+  addNotificationJob: vi.fn(() => Promise.resolve()),
+  addDownloadJob: vi.fn(),
 }));
 const findPlexMatchMock = vi.hoisted(() => vi.fn());
 
@@ -269,17 +271,28 @@ describe('Request Approval Workflow', () => {
         audiobook: { asin: 'ASIN-7', title: 'Test Book', author: 'Test Author' },
       });
 
+      // Mock first request.findFirst call (check for existing requests by ASIN)
+      prismaMock.request.findFirst.mockResolvedValueOnce(null);
+      // Mock findPlexMatch
+      findPlexMatchMock.mockResolvedValueOnce(null);
+      // Mock audiobook.findFirst
+      prismaMock.audiobook.findFirst.mockResolvedValueOnce(null);
+
       prismaMock.audiobook.create.mockResolvedValueOnce({
         id: 'ab-7',
         title: 'Test Book',
         author: 'Test Author',
         audibleAsin: 'ASIN-7',
-      });
+      } as any);
+
+      // Mock second request.findFirst call (check for user's existing request)
+      prismaMock.request.findFirst.mockResolvedValueOnce(null);
 
       prismaMock.user.findUnique.mockResolvedValue({
         id: 'user-1',
         role: 'user',
         autoApproveRequests: true,
+        plexUsername: 'testuser',
       } as any);
 
       prismaMock.request.create.mockResolvedValue({
@@ -520,6 +533,7 @@ describe('Request Approval Workflow', () => {
       prismaMock.request.findUnique.mockResolvedValue({
         id: 'req-1',
         status: 'awaiting_approval',
+        selectedTorrent: null,
         userId: 'user-1',
         audiobook: { id: 'ab-1', title: 'Test Book', author: 'Test Author', audibleAsin: 'ASIN-1' },
         user: { id: 'user-1', plexUsername: 'testuser' },
@@ -569,6 +583,7 @@ describe('Request Approval Workflow', () => {
       prismaMock.request.findUnique.mockResolvedValue({
         id: 'req-2',
         status: 'awaiting_approval',
+        selectedTorrent: null,
         userId: 'user-1',
         audiobook: { id: 'ab-2', title: 'Test Book 2', author: 'Test Author 2', audibleAsin: 'ASIN-2' },
         user: { id: 'user-1', plexUsername: 'testuser' },