Meta Per Book Sla

Per-book freshness SLA thresholds. Public, no auth, no credits.

Returns the (tight_s, slack_s, stale_s) thresholds used to classify each source as ok / degraded / breach / stale in the source-quality payloads. Customers integrating against /v1/meta/source-quality use this to know what sla=degraded actually means for a given book (e.g. "Pinnacle tight=5s, Bovada tight=30s, PrizePicks tight=60s").

Memory rule compliance: read-only on already-public threshold config. No prices touched.