feat: integrate Datadog APM + Sentry error tracking with CloudWatch metrics FRE-4806

- Add CloudWatch metrics emitter (api_latency, api_requests, api_errors)
- Add request monitoring middleware for API (latency, error rate, throughput)
- Register error-handling, logging, and monitoring middleware in server.ts
- Add Datadog log forwarding via HTTP intake API
- Add application-level CloudWatch alarms for P99 latency, error rate, throughput
- Inject Datadog/Sentry env vars and secrets into ECS task definitions
- Add DD_API_KEY and SENTRY_DSN to ECS secrets
- Create CloudWatch log groups for datadog and sentry services
- Update .env.example with AWS_REGION and monitoring variables
- Add @aws-sdk/client-cloudwatch dependency to monitoring package

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.env.example

@@ -4,3 +4,22 @@ PORT=3000
 LOG_LEVEL=info
 HIBP_API_KEY=""
 RESEND_API_KEY=""
+AWS_REGION="us-east-1"
+
+# Datadog APM Configuration
+DD_SERVICE="shieldai-api"
+DD_ENV="development"
+DD_VERSION="0.1.0"
+DD_TRACE_ENABLED="true"
+DD_TRACE_SAMPLE_RATE="1.0"
+DD_LOGS_INJECTION="true"
+DD_AGENT_HOST="localhost"
+DD_AGENT_PORT="8126"
+DD_API_KEY=""
+DD_SITE="datadoghq.com"
+
+# Sentry Error Tracking
+SENTRY_DSN=""
+SENTRY_ENVIRONMENT="development"
+SENTRY_RELEASE="0.1.0"
+SENTRY_TRACES_SAMPLE_RATE="0.1"