security: add safe.ReadAllLimited — bound all HTTP response body reads to 10MB

- Created safe/io.go with ReadAllLimited helper (default 10MB limit)
- Replaced 62 unbounded io.ReadAll(resp.Body) calls across 32 files
- Covers all exchange traders (Hyperliquid, Bybit, Binance, OKX, Aster,
  KuCoin, Gate, Bitget, Lighter, Indodax), providers (CoinAnk, Alpaca,
  TwelveData), MCP client/x402, market data, wallet, telegram, kernel
- Prevents OOM from malicious/buggy exchange API responses
- Previously fixed: brain.go, sentinel.go already had manual LimitReader

kernel/engine.go

@@ -1,10 +1,10 @@
 package kernel
 
 import (
+	"nofx/safe"
 	"context"
 	"encoding/json"
 	"fmt"
-	"io"
 	"net/http"
 	"nofx/logger"
 	"nofx/market"
@@ -616,7 +616,7 @@ func (e *StrategyEngine) fetchSingleExternalSource(source store.ExternalDataSour
 	}
 	defer resp.Body.Close()
 
-	body, err := io.ReadAll(resp.Body)
+	body, err := safe.ReadAllLimited(resp.Body)
 	if err != nil {
 		return nil, err
 	}