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/helpers.go

@@ -5,6 +5,19 @@ import (
 	"strconv"
 )
 
+// posFloat64 extracts a float64 from a position map, returning 0 on failure.
+// Use in loops where a malformed position should be skipped, not crash.
+func posFloat64(pos map[string]interface{}, key string) float64 {
+	v, _ := SafeFloat64(pos, key)
+	return v
+}
+
+// posString extracts a string from a position map, returning "" on failure.
+func posString(pos map[string]interface{}, key string) string {
+	v, _ := SafeString(pos, key)
+	return v
+}
+
 // SafeFloat64 Safely extract float64 value from map
 func SafeFloat64(data map[string]interface{}, key string) (float64, error) {
 	value, ok := data[key]