Complete Polymarket trading skill for prediction markets on Polygon. Use when user wants to onboard, trade (buy/sell, market/limit), check balance, view holdings/positions, manage orders (active/cancel), or check rewards. Handles credential setup, balance verification, and all trading operations on Polymarket CLOB. REQUIRES polymarket skill (poly-gamma-skills) for market discovery to get clobTokenIds. REQUIRES polymarket-data-api skill for user portfolio/P&L data.