Monitoring: Enhance alerting and security #1271

Description
Monitoring currently lacks proper alerting, and the dashboard needs to be more secure and reliable. This issue covers connecting CloudWatch alarms to SNS email notifications and hardening the monitoring dashboard.

Tasks

• Create an SNS topic (e.g. monitoring-alerts)
• Subscribe team email addresses to the topic and confirm the subscriptions
• Create CloudWatch alarms for key metrics (CPU, memory, disk, 5xx errors, latency)
• Connect the alarms to the SNS topic
• Send a test alert to verify emails are delivered
• Restrict dashboard access using IAM (least privilege)
• Add or clean up dashboard widgets for key metrics and alarm status
• Review log retention and alarm thresholds
• Document the setup in the README/docs