fix: prevent panics from unsafe type assertions in trading code + add request body limit

Security & Reliability:
- Add requestBodyLimitMiddleware (1MB) to prevent OOM from oversized API payloads
- Fix defer resp.Body.Close() inside loop in getPublicIPFromAPI (connection leak)
- Add posFloat64/posString safe helpers for position map access

Panic Prevention (critical for trading):
- Convert 30+ unsafe type assertions (pos["key"].(type)) to safe comma-ok
  pattern across all exchange traders: OKX, Hyperliquid, Aster, Bybit,
  KuCoin, Gate, Bitget, Binance
- Fix auto_trader_risk.go: drawdown monitor could panic and silently stop
  monitoring, leaving positions unprotected
- Fix auto_trader_decision.go & auto_trader_loop.go: core trading loop
  position parsing now crash-proof
- All trader/ code now has zero unsafe type assertions

Frontend:
- Fix config.ts: rejected promise cached forever on network error (never retries)

trader/binance/futures_orders.go

@@ -131,7 +131,7 @@ func (t *FuturesTrader) CloseLong(symbol string, quantity float64) (map[string]i
 
 		for _, pos := range positions {
 			if pos["symbol"] == symbol && pos["side"] == "long" {
-				quantity = pos["positionAmt"].(float64)
+				quantity, _ = pos["positionAmt"].(float64)
 				break
 			}
 		}

trader/binance/futures_positions.go

@@ -227,7 +227,7 @@ func (t *FuturesTrader) GetSymbolPrecision(symbol string) (int, error) {
 			// Get precision from LOT_SIZE filter
 			for _, filter := range s.Filters {
 				if filter["filterType"] == "LOT_SIZE" {
-					stepSize := filter["stepSize"].(string)
+					stepSize, _ := filter["stepSize"].(string)
 					precision := calculatePrecision(stepSize)
 					logger.Infof("  %s quantity precision: %d (stepSize: %s)", symbol, precision, stepSize)
 					return precision, nil
@@ -264,7 +264,7 @@ func (t *FuturesTrader) GetSymbolPricePrecision(symbol string) (int, error) {
 			// Get precision from PRICE_FILTER filter
 			for _, filter := range s.Filters {
 				if filter["filterType"] == "PRICE_FILTER" {
-					tickSize := filter["tickSize"].(string)
+					tickSize, _ := filter["tickSize"].(string)
 					precision := calculatePrecision(tickSize)
 					return precision, nil
 				}