feat: update adaptor methods and add new image model

relay/channel/xai/constants.go

@@ -8,7 +8,9 @@ var ModelList = []string{
 	// extend grok-3-mini reasoning
 	"grok-3-mini-beta-high", "grok-3-mini-beta-low", "grok-3-mini-beta-medium",
 	"grok-3-mini-fast-beta-high", "grok-3-mini-fast-beta-low", "grok-3-mini-fast-beta-medium",
-
+	// image model
+	"grok-2-image",
+	// legacy models
 	"grok-2", "grok-2-vision",
 	"grok-beta", "grok-vision-beta",
 }