Remove unprofitable 15m timeframe symbols (ETHUSDT & EURUSD) from the entire application

Apply user's multi-key Twelve Data integration for Forex/Metals with dedicated polling cycles and Yahoo fallback routing

Completely remove and clean up Twelve Data integration from the codebase

Lower Forex outlier wick filter to 40 pips and implement same filter in twelveDataAPI

feat: implement Twelve Data provider integration with secure Express API proxy, automated server-side caching, and key-activated OANDA spot gold/forex upgrade