fix: default transport client in clob.NewClient when httpClient is nil

gamma.NewClient and data.NewClient both create a default transport when
passed nil, but clob.NewClient stored the nil pointer directly, causing
a nil dereference panic on any subsequent API call.

Add BaseURL constant and a nil guard matching the gamma/data pattern.

Author: 0x4139

pkg/clob/constants.go

@@ -1,6 +1,9 @@
 package clob
 
 const (
+	// BaseURL is the default production endpoint for the CLOB.
+	BaseURL = "https://clob.polymarket.com"
+
 	// DefaultGeoblockHost is the default host for the geoblock endpoint.
 	DefaultGeoblockHost = "https://polymarket.com"
 )

pkg/clob/impl.go

@@ -71,6 +71,10 @@ func NewClientWithGeoblock(httpClient *transport.Client, geoblockHost string) Cl
 		geoblockHost = DefaultGeoblockHost
 	}
 
+	if httpClient == nil {
+		httpClient = transport.NewClient(nil, BaseURL)
+	}
+
 	c := &clientImpl{
 		httpClient:     httpClient,
 		cache:          newClientCache(),