Frontend API_BASE is /api in production, so health check was hitting
/api/health which didn't exist. Added /api/health on the server and
removed the now-unnecessary separate nginx /health proxy rule.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
The frontend builds with VITE_API_URL=/api so all API calls target
the same origin. Without a proxy rule, nginx was serving index.html
for API paths, causing JSON parse errors.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>