Add PM2 restart_delay and max_restarts to prevent crash-loop spam

When DB_PASSWORD is missing on startup, server exits and PM2 was
restarting every ~660ms flooding backend.log with ER_ACCESS_DENIED_ERROR.
Now waits 5s between restarts and caps at 10 attempts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

database/pm2.config.js

@@ -5,6 +5,8 @@ module.exports = {
       script: './server.js',
       cwd: __dirname,
       watch: false,
+      restart_delay: 5000,
+      max_restarts: 10,
       env: {
         NODE_ENV: 'production',
         PORT: 5000,