fix(trader): harden API calls with timeouts, strict balance parsing, error context

- binance/bybit/gate: SDK default http.DefaultClient has no timeout; use a
  dedicated 30s-timeout client so a hung connection cannot stall the loop
- bybit: stop mutating http.DefaultClient.Transport, which leaked the
  referer header into every other HTTP request in the process
- add types.ParseFloatField: empty exchange fields stay zero, but malformed
  numeric values now surface as errors instead of silently becoming zero
  balances (applied to GetBalance across 8 exchanges)
- wrap order/market-data errors in auto_trader_orders and okx cancel paths
  with symbol context; log per-order cancel failures in okx CancelAllOrders

trader/gate/trader.go

@@ -3,6 +3,7 @@ package gate
 import (
 	"context"
 	"fmt"
+	"net/http"
 	"nofx/trader/types"
 	"strings"
 	"sync"
@@ -34,6 +35,9 @@ type GateTrader struct {
 func NewGateTrader(apiKey, secretKey string) *GateTrader {
 	config := gateapi.NewConfiguration()
 	config.AddDefaultHeader("X-Gate-Channel-Id", "nofx")
+	// The SDK default HTTP client has no timeout — a hung connection would
+	// stall the trading loop indefinitely.
+	config.HTTPClient = &http.Client{Timeout: 30 * time.Second}
 	client := gateapi.NewAPIClient(config)
 
 	ctx := context.WithValue(context.Background(),

trader/gate/trader_account.go

@@ -27,9 +27,18 @@ func (t *GateTrader) GetBalance() (map[string]interface{}, error) {
 		return nil, fmt.Errorf("failed to get balance: %w", err)
 	}
 
-	total, _ := strconv.ParseFloat(accounts.Total, 64)
-	available, _ := strconv.ParseFloat(accounts.Available, 64)
-	unrealizedPnl, _ := strconv.ParseFloat(accounts.UnrealisedPnl, 64)
+	total, err := types.ParseFloatField("total", accounts.Total)
+	if err != nil {
+		return nil, err
+	}
+	available, err := types.ParseFloatField("available", accounts.Available)
+	if err != nil {
+		return nil, err
+	}
+	unrealizedPnl, err := types.ParseFloatField("unrealisedPnl", accounts.UnrealisedPnl)
+	if err != nil {
+		return nil, err
+	}
 
 	result := map[string]interface{}{
 		"totalWalletBalance":    total,