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/auto_trader_risk.go

@@ -41,11 +41,14 @@ func (at *AutoTrader) checkPositionDrawdown() {
 	}
 
 	for _, pos := range positions {
-		symbol := pos["symbol"].(string)
-		side := pos["side"].(string)
-		entryPrice := pos["entryPrice"].(float64)
-		markPrice := pos["markPrice"].(float64)
-		quantity := pos["positionAmt"].(float64)
+		symbol, _ := pos["symbol"].(string)
+		side, _ := pos["side"].(string)
+		entryPrice, _ := pos["entryPrice"].(float64)
+		markPrice, _ := pos["markPrice"].(float64)
+		quantity, _ := pos["positionAmt"].(float64)
+		if symbol == "" || side == "" || entryPrice == 0 {
+			continue // skip malformed position data
+		}
 		if quantity < 0 {
 			quantity = -quantity // Short position quantity is negative, convert to positive
 		}