Upstream service health check

GET /health · No API key needed

Pings Supabase, Cohere, Groq, and Open Food Facts in parallel. Reports per-service status plus an overall healthy/degraded verdict. Open Food Facts is live-pinged too (free/keyless) but, like USDA FDC/FatSecret/the rate-limit KV (reported as configured/bound without a network call), it's visibility-only and doesn't affect the overall verdict.