fix: require namespace for workflow operations, return 400 if missing

Temporal handler was defaulting to 'default' namespace when not provided.
CI test expects 400 for missing namespace. Validate before forwarding.

internal/serviceadapter/workflow_adapter.go

@@ -134,8 +134,13 @@ func (wa *WorkflowAdapter) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 	// Inject action into body for temporal handler
 	payload["action"] = action
-	if _, ok := payload["namespace"]; !ok {
-		payload["namespace"] = "default"
+
+	// namespace is required for all workflow operations
+	if ns, ok := payload["namespace"].(string); !ok || ns == "" {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusBadRequest)
+		fmt.Fprintf(w, `{"error":"namespace is required"}`)
+		return
 	}
 
 	newBody, _ := json.Marshal(payload)