Revert react-router v7 future flags from #31818

Roll back the v7_relativeSplatPath and v7_startTransition future flags
and the Outlet-based route structure, keeping the version bump to
react-router-dom@^6.30.2.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

plugins/app/src/extensions/AppRoot.tsx

@@ -198,17 +198,7 @@ export interface AppRouterProps {
 function DefaultRouter(props: PropsWithChildren<{}>) {
   const configApi = useApi(configApiRef);
   const basePath = getBasePath(configApi);
-  return (
-    <BrowserRouter
-      basename={basePath}
-      future={{
-        v7_relativeSplatPath: true,
-        v7_startTransition: true,
-      }}
-    >
-      {props.children}
-    </BrowserRouter>
-  );
+  return <BrowserRouter basename={basePath}>{props.children}</BrowserRouter>;
 }
 
 /**

plugins/app/src/extensions/AppRoutes.tsx

@@ -20,7 +20,7 @@ import {
   createExtensionInput,
   NotFoundErrorPage,
 } from '@backstage/frontend-plugin-api';
-import { useRoutes, Outlet } from 'react-router-dom';
+import { useRoutes } from 'react-router-dom';
 
 export const AppRoutes = createExtension({
   name: 'routes',
@@ -38,42 +38,14 @@ export const AppRoutes = createExtension({
       const element = useRoutes([
         ...inputs.routes.map(route => {
           const routePath = route.get(coreExtensionData.routePath);
-          const routeElement = route.get(coreExtensionData.reactElement);
 
-          // For v7_relativeSplatPath: convert splat paths to parent/child structure
-          if (routePath === '/') {
-            // Root route: parent with index and splat children
-            return {
-              path: '/',
-              element: <Outlet />,
-              children: [
-                {
-                  index: true,
-                  element: routeElement,
-                },
-                {
-                  path: '*',
-                  element: routeElement,
-                },
-              ],
-            };
-          }
-
-          // Non-root routes: parent route with splat child
-          const normalizedPath = routePath.replace(/\/$/, '');
           return {
-            path: normalizedPath,
-            element: <Outlet />,
-            children: [
-              {
-                index: true,
-                element: routeElement,
-              },
-              {
-                path: '*',
-                element: routeElement,
-              },
-            ],
+            path:
+              routePath === '/'
+                ? routePath
+                : `${routePath.replace(/\/$/, '')}/*`,
+
+            element: route.get(coreExtensionData.reactElement),
           };
         }),
         {