fix(hyperliquid): stop SDK init panic from crashing trader creation with 500

go-hyperliquid's NewExchange auto-fetches meta/spotMeta/perpDexs and
panics if any of those API calls fail (NewInfo: panic(err)). The quick
trade flow constructs a probe trader inside POST /api/traders, so any
transient Hyperliquid API hiccup crashed the request with a recovered
panic and a bare 500. Wrap the constructor in initExchangeClient, which
converts the panic into an error that surfaces through the existing
exchange-probe validation path as an honest, retryable message.

trader/hyperliquid/client_init_test.go

@@ -0,0 +1,37 @@
+package hyperliquid
+
+import (
+	"errors"
+	"strings"
+	"testing"
+
+	hl "github.com/sonirico/go-hyperliquid"
+)
+
+func TestInitExchangeClientConvertsPanicToError(t *testing.T) {
+	// The SDK constructor panics when its automatic meta fetch fails
+	// (go-hyperliquid info.go NewInfo: panic(err)). The wrapper must turn
+	// that into an error instead of crashing the HTTP handler.
+	_, err := initExchangeClient(func() *hl.Exchange {
+		panic(errors.New("failed to fetch meta: API error 0: "))
+	})
+	if err == nil {
+		t.Fatal("expected error when the SDK constructor panics, got nil")
+	}
+	if !strings.Contains(err.Error(), "failed to fetch meta") {
+		t.Errorf("error should carry the panic cause, got %q", err.Error())
+	}
+}
+
+func TestInitExchangeClientPassesThroughSuccess(t *testing.T) {
+	want := &hl.Exchange{}
+	got, err := initExchangeClient(func() *hl.Exchange {
+		return want
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != want {
+		t.Fatal("wrapper must return the constructed exchange unchanged")
+	}
+}