Refactor workflow state management in site building; enhance error handling and field validation in models and serializers. Remove obsolete workflow components from frontend and adjust API response structure for clarity.

frontend/src/App.tsx

@@ -99,7 +99,6 @@ const DeploymentPanel = lazy(() => import("./pages/Sites/DeploymentPanel"));
 
 // Site Builder - Lazy loaded (will be moved from separate container)
 const SiteBuilderWizard = lazy(() => import("./pages/Sites/Builder/Wizard"));
-const WorkflowWizard = lazy(() => import("./pages/Sites/Builder/WorkflowWizard"));
 const SiteBuilderPreview = lazy(() => import("./pages/Sites/Builder/Preview"));
 const SiteBuilderBlueprints = lazy(() => import("./pages/Sites/Builder/Blueprints"));
 
@@ -524,11 +523,6 @@ export default function App() {
                 <SiteBuilderWizard />
               </Suspense>
             } />
-            <Route path="/sites/builder/workflow/:blueprintId" element={
-              <Suspense fallback={null}>
-                <WorkflowWizard />
-              </Suspense>
-            } />
             <Route path="/sites/builder/preview" element={
               <Suspense fallback={null}>
                 <SiteBuilderPreview />