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/send-notification.processor.ts

@@ -0,0 +1,55 @@
+/**
+ * Component: Send Notification Job Processor
+ * Documentation: documentation/backend/services/notifications.md
+ *
+ * Processes notification jobs by calling NotificationService to send alerts
+ * to all enabled backends subscribed to the event.
+ */
+
+import { getNotificationService } from '../services/notification.service';
+import { RMABLogger } from '../utils/logger';
+
+export interface SendNotificationPayload {
+  jobId?: string;
+  event: 'request_pending_approval' | 'request_approved' | 'request_available' | 'request_error';
+  requestId: string;
+  title: string;
+  author: string;
+  userName: string;
+  message?: string;
+  timestamp: Date;
+}
+
+/**
+ * Process send notification job
+ * Calls NotificationService to send notifications to all enabled backends
+ */
+export async function processSendNotification(payload: SendNotificationPayload): Promise<void> {
+  const { event, requestId, title, author, userName, message, jobId } = payload;
+
+  const logger = RMABLogger.forJob(jobId, 'SendNotification');
+
+  logger.info(`Processing notification: ${event}`, { requestId });
+
+  try {
+    const notificationService = getNotificationService();
+    await notificationService.sendNotification({
+      event,
+      requestId,
+      title,
+      author,
+      userName,
+      message,
+      timestamp: new Date(),
+    });
+
+    logger.info(`Notification processed: ${event}`, { requestId });
+  } catch (error) {
+    logger.error('Failed to process notification', {
+      event,
+      requestId,
+      error: error instanceof Error ? error.message : String(error),
+    });
+    // Don't throw - non-blocking
+  }
+}