feat(frontend): move task creation to dedicated page with scrollable layout

Replace the EntityDetailPage modal flow with a route-based CreateTaskPage for better accessibility and long-form usability.

Add route /entities/:entityId/tasks/new and update tests for both entity detail navigation and create-task page behavior.

frontend/src/router/index.tsx

@@ -7,6 +7,7 @@ const LoginPage = lazy(() => import('../pages/LoginPage'))
 const DashboardPage = lazy(() => import('../pages/DashboardPage'))
 const EntitiesPage = lazy(() => import('../pages/EntitiesPage'))
 const EntityDetailPage = lazy(() => import('../pages/EntityDetailPage'))
+const CreateTaskPage = lazy(() => import('../pages/CreateTaskPage'))
 const LogsPage = lazy(() => import('../pages/LogsPage'))
 
 function Protected({ children }: { children: ReactNode }) {
@@ -55,6 +56,14 @@ export const router = createBrowserRouter([
       </Protected>
     ),
   },
+  {
+    path: '/entities/:entityId/tasks/new',
+    element: (
+      <Protected>
+        <CreateTaskPage />
+      </Protected>
+    ),
+  },
   {
     path: '/logs',
     element: (