Current price + daily % change for specific stock symbols.

    Args:
        tickers: comma-separated EXCHANGE:SYMBOL list (max 2000 — one
            upstream request even at full size), e.g.
            "NASDAQ:NVDA, NASDAQ:TSLA, KRX:005930". The exchange prefix is
            required — the scanner's direct-ticker lookup is exchange-scoped.

    Returns:
        Envelope dict: rows of {ticker, symbol, description, exchange, price,
        open, high, low, currency, change_percent} plus a not_found list naming any requested
        ticker the scanner didn't recognize.