fix: database connection stability issues in production

- Add robust connection pool configuration with timeouts and retry settings
- Implement retry logic in maintenance middleware for connection errors
- Increase connection stability with keepAlive and proper timeout values
- Handle "Connection terminated unexpectedly" errors gracefully

This prevents 503 errors when the database connection is temporarily interrupted
and ensures the application can recover from transient connection issues.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/src/database/db.js

@@ -1,6 +1,7 @@
 const knex = require('knex');
 const knexConfig = require('../../knexfile');
 
+// Create database connection with built-in retry logic
 const db = knex(knexConfig);
 
 async function initializeDatabase() {