Dataset-wide freshness for NHL player props

Answers "is the NHL props dataset live right now" with no player or market, for a build-time reader (e.g. marketing copy) that cannot supply either. Returns the SAME freshness shape documented on GET /v1/nhl/players/{player_id}/props, derived from MAX(fetched_at) across every held NHL prop line rather than one player's line: data_as_of, age_days, status (live ≤2d, recent ≤14d, stale >14d, or no_data when the table is empty), and note. A page reading this can never claim live while the per-player endpoint would call the same data stale.