List supported sports + their leagues

Returns the canonical list of sport codes accepted by every other endpoint (nba, euroleague, football, tennis for ATP men's tennis, wta for WTA women's tennis, champions for the UEFA Champions League) plus, where applicable, the list of league codes that can be passed as ?league= on football endpoints. Coverage is not uniform: champions exposes season simulations (/v1/simulations/champions), per-match 1X2 predictions (/v1/predictions/champions/..., league phase onward only — qualifying is never published), per-player track records (/v1/players/champions/{player}/prediction-performance), model performance (/v1/performance/champions?source=backtest) and calibration; /v1/ratings answers 404 for it. The set is stable; new entries are additive within v1.