feat: add claude-opus-4-6

relay/channel/vertex/adaptor.go

@@ -42,6 +42,7 @@ var claudeModelMap = map[string]string{
 	"claude-sonnet-4-5-20250929": "claude-sonnet-4-5@20250929",
 	"claude-haiku-4-5-20251001":  "claude-haiku-4-5@20251001",
 	"claude-opus-4-5-20251101":   "claude-opus-4-5@20251101",
+	"claude-opus-4-6":            "claude-opus-4-6",
 }
 
 const anthropicVersion = "vertex-2023-10-16"