fix: Alpaca integration bugs — field mapping, market hours, stock symbol handling

- Fix critical bug: Alpaca GetBalance returns wrong field names (total_equity
  vs totalEquity) — auto_trader was getting 0 equity, breaking all decisions
- Fix critical bug: Alpaca GetPositions missing positionAmt/unRealizedProfit
  fields — positions invisible to trading AI
- Fix CancelAllOrders: was nuking ALL orders globally, now filters by symbol
- Implement GetClosedPnL: was returning nil, now returns filled sell orders
- Add IsMarketOpen: checks Alpaca clock endpoint for market hours
- Add market hours check in trading loop: skip cycles when US market closed
  (saves LLM tokens and prevents failed orders)
- Fix parseTradeCommand: 'BUY AAPL 10' no longer becomes 'AAPLUSDT'
- Fix toolGetMarketPrice: route stock symbols to Alpaca, crypto to others
- Add exchange field to toolGetPositions output for multi-exchange clarity

agent/tools.go

@@ -274,6 +274,7 @@ func (a *Agent) toolGetPositions() string {
 			}
 			positions = append(positions, map[string]any{
 				"trader":          tid,
+				"exchange":        t.GetExchange(),
 				"symbol":          p["symbol"],
 				"side":            p["side"],
 				"size":            size,
@@ -339,11 +340,20 @@ func (a *Agent) toolGetMarketPrice(argsJSON string) string {
 		return `{"error": "no trader manager configured"}`
 	}
 
+	wantStock := isStockSymbol(sym)
 	for _, t := range a.traderManager.GetAllTraders() {
 		underlying := t.GetUnderlyingTrader()
 		if underlying == nil {
 			continue
 		}
+		// Route to correct exchange type (stock vs crypto)
+		isAlpaca := t.GetExchange() == "alpaca"
+		if wantStock && !isAlpaca {
+			continue
+		}
+		if !wantStock && isAlpaca {
+			continue
+		}
 		price, err := underlying.GetMarketPrice(sym)
 		if err == nil && price > 0 {
 			result, _ := json.Marshal(map[string]any{