Fix issues #49 and #50: Migration errors and missing worker manager

- Fix #49: Add column existence checks to migration 011_add_user_upload_settings.js
  to prevent "column already exists" errors during deployment
- Fix #50: Create missing workerManager.js file that starts background services
  (file watcher and expiration checker) for native installations

backend/src/services/workerManager.js

@@ -0,0 +1,72 @@
+/**
+ * Worker Manager - Background service for PicPeak
+ *
+ * This service runs as a separate process to handle:
+ * - File watching for new photos
+ * - Expiration checking for events
+ * - Other background tasks
+ */
+
+const path = require('path');
+const logger = require('../utils/logger');
+
+// Load environment variables
+require('dotenv').config({ path: path.join(__dirname, '../../.env') });
+
+// Import services
+const { startFileWatcher } = require('./fileWatcher');
+const { startExpirationChecker } = require('./expirationChecker');
+
+let isShuttingDown = false;
+
+async function startWorkers() {
+  logger.info('Starting PicPeak background workers...');
+
+  try {
+    // Start file watcher for automatic photo processing
+    startFileWatcher();
+    logger.info('File watcher started successfully');
+
+    // Start expiration checker for event lifecycle management
+    startExpirationChecker();
+    logger.info('Expiration checker started successfully');
+
+    logger.info('All background workers started successfully');
+  } catch (error) {
+    logger.error('Failed to start background workers:', error);
+    process.exit(1);
+  }
+}
+
+function handleShutdown(signal) {
+  if (isShuttingDown) {
+    logger.info('Shutdown already in progress...');
+    return;
+  }
+
+  isShuttingDown = true;
+  logger.info(`Received ${signal}. Shutting down gracefully...`);
+
+  // Give time for cleanup
+  setTimeout(() => {
+    logger.info('Worker manager shutdown complete');
+    process.exit(0);
+  }, 1000);
+}
+
+// Handle shutdown signals
+process.on('SIGTERM', () => handleShutdown('SIGTERM'));
+process.on('SIGINT', () => handleShutdown('SIGINT'));
+
+// Handle uncaught errors
+process.on('uncaughtException', (error) => {
+  logger.error('Uncaught exception in worker manager:', error);
+  process.exit(1);
+});
+
+process.on('unhandledRejection', (reason, promise) => {
+  logger.error('Unhandled rejection in worker manager:', reason);
+});
+
+// Start workers
+startWorkers();