Historical OHLC candles for a crypto pair (e.g. BTC-USD) — for technical analysis and backtesting. Query: pair; granularity (1m, 5m, 15m, 1h, 6h, 1d — default 1h); limit (1-300, default 100) for the latest window, OR start & end (ISO8601 or unix secs) for a backtest range paginated server-side up to 3000 candles — months of history in one call. Returns candles oldest->newest, each {t, o, h, l, c, v}. Real-time from Coinbase.