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_loop.go

@@ -331,11 +331,11 @@ func (at *AutoTrader) buildTradingContext() (*kernel.Context, error) {
 	currentPositionKeys := make(map[string]bool)
 
 	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 := posString(pos, "symbol")
+		side := posString(pos, "side")
+		entryPrice := posFloat64(pos, "entryPrice")
+		markPrice := posFloat64(pos, "markPrice")
+		quantity := posFloat64(pos, "positionAmt")
 		if quantity < 0 {
 			quantity = -quantity // Short position quantity is negative, convert to positive
 		}
@@ -345,8 +345,8 @@ func (at *AutoTrader) buildTradingContext() (*kernel.Context, error) {
 			continue
 		}
 
-		unrealizedPnl := pos["unRealizedProfit"].(float64)
-		liquidationPrice := pos["liquidationPrice"].(float64)
+		unrealizedPnl := posFloat64(pos, "unRealizedProfit")
+		liquidationPrice := posFloat64(pos, "liquidationPrice")
 
 		// Calculate margin used (estimated)
 		leverage := 10 // Default value, should actually be fetched from position info