feat: add New Relic APM instrumentation to backend

Add Node.js New Relic agent with an on/off switch via NEW_RELIC_ENABLED
in .env. Uses a preload script (-r newrelic-preload.js) so the agent
loads before all other modules. Configured entirely through environment
variables — no newrelic.js config file needed.

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

docker-compose.yml

@@ -26,6 +26,9 @@ services:
       - AI_API_KEY=${AI_API_KEY}
       - AI_MODEL=${AI_MODEL}
       - AI_DEBUG=${AI_DEBUG:-false}
+      - NEW_RELIC_ENABLED=${NEW_RELIC_ENABLED:-false}
+      - NEW_RELIC_LICENSE_KEY=${NEW_RELIC_LICENSE_KEY:-}
+      - NEW_RELIC_APP_NAME=${NEW_RELIC_APP_NAME:-HOALedgerIQ_App}
     volumes:
       - ./backend/src:/app/src
       - ./backend/nest-cli.json:/app/nest-cli.json