Query real-time stablecoin supply yield pools from Barker's index of 500+ DeFi protocols. Returns ranked rows with protocol_name, chain_name, asset_symbol, supply_apy_total (decimal — multiply by 100 for %), and supply_tvl (USD). Use for questions like 'best stablecoin yield', 'where to earn on USDC', 'compare lending rates', '稳定币利率'.