feat(gantt): introduce advanced Gantt chart components and demo page

- Added new components for an advanced Gantt chart, including AdvancedGanttChart, GanttGrid, DraggableTaskBar, and TimelineMarkers.
- Implemented a demo page (GanttDemoPage) to showcase the functionality of the new Gantt chart components.
- Enhanced project roadmap features with ProjectRoadmapGantt and related components for better project management visualization.
- Introduced sample data for testing and demonstration purposes, improving the user experience in the Gantt chart interface.
- Updated main routes to include the new Gantt demo page for easy access.

worklenz-frontend/src/app/routes/main-routes.tsx

@@ -17,6 +17,7 @@ const ProjectTemplateEditView = lazy(
 const LicenseExpired = lazy(() => import('@/pages/license-expired/license-expired'));
 const ProjectView = lazy(() => import('@/pages/projects/projectView/project-view'));
 const Unauthorized = lazy(() => import('@/pages/unauthorized/unauthorized'));
+const GanttDemoPage = lazy(() => import('@/pages/GanttDemoPage'));
 
 // Define AdminGuard component with defensive programming
 const AdminGuard = ({ children }: { children: React.ReactNode }) => {
@@ -106,6 +107,14 @@ const mainRoutes: RouteObject[] = [
           </Suspense>
         ),
       },
+      {
+        path: 'gantt-demo',
+        element: (
+          <Suspense fallback={<SuspenseFallback />}>
+            <GanttDemoPage />
+          </Suspense>
+        ),
+      },
       ...settingsRoutes,
       ...adminCenterRoutes,
     ],