Add comprehensive database setup and user management system

- Implement PostgreSQL database schema with users and bookmarks tables
- Add database connection pooling with retry logic and error handling
- Create migration system with automatic schema initialization
- Add database CLI tools for management (init, status, validate, etc.)
- Include comprehensive error handling and diagnostics
- Add development seed data and testing utilities
- Implement health monitoring and connection pool statistics
- Create detailed documentation and troubleshooting guide

Database features:
- Users table with authentication fields and email verification
- Bookmarks table with user association and metadata
- Proper indexes for performance optimization
- Automatic timestamp triggers
- Transaction support with rollback handling
- Connection pooling (20 max connections, 30s idle timeout)
- Graceful shutdown handling

CLI commands available:
- npm run db:init - Initialize database
- npm run db:status - Check database status
- npm run db:validate - Validate schema
- npm run db:test - Run database tests
- npm run db:diagnostics - Full diagnostics

backend/server.js

@@ -0,0 +1,45 @@
+const app = require('./src/app');
+const dbInitializer = require('./src/database/init');
+const dbConnection = require('./src/database/connection');
+
+const PORT = process.env.PORT || 3001;
+
+// Initialize database and start server
+async function startServer() {
+  try {
+    console.log('🚀 Starting Bookmark Manager Backend...');
+    
+    // Initialize database
+    await dbInitializer.initialize();
+    
+    // Start the server
+    const server = app.listen(PORT, () => {
+      console.log(`✅ Server is running on port ${PORT}`);
+      console.log(`🌍 Environment: ${process.env.NODE_ENV || 'development'}`);
+      console.log(`🔗 Health check: http://localhost:${PORT}/health`);
+    });
+
+    // Graceful shutdown handling
+    process.on('SIGTERM', async () => {
+      console.log('🛑 SIGTERM received, shutting down gracefully...');
+      server.close(async () => {
+        await dbConnection.close();
+        process.exit(0);
+      });
+    });
+
+    process.on('SIGINT', async () => {
+      console.log('🛑 SIGINT received, shutting down gracefully...');
+      server.close(async () => {
+        await dbConnection.close();
+        process.exit(0);
+      });
+    });
+
+  } catch (error) {
+    console.error('❌ Failed to start server:', error);
+    process.exit(1);
+  }
+}
+
+startServer();