Five env vars, all with defaults sized for this deployment (84 series
at a 1h cadence). Bad values log and fall back rather than failing
startup, and the cooldown is floored at 15m. Fetches go through
tls-client with a Chrome profile as defence in depth.
tls-client v1.15.1 declares go 1.24.1; every release back to v1.13.0
does the same, so the 1.23 floor cannot stay. Pure Go, so the
CGO_ENABLED=0 static build and distroless image are unchanged.