Locks down AC1: prometheus-fastapi-instrumentator must keep auto-exposing
http_requests_total and http_request_duration_seconds for application
traffic, not just register the /metrics endpoint.
Refs #652
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Mount the instrumentator immediately after FastAPI app creation, excluding
/health and /metrics from request metrics to keep http_requests_total focused
on real application traffic.
Refs #652
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>