Add front component skeleton loader (#23261)

Front components (dashboard widget, side panel, settings preview) showed
blank space during their entire load. They now show a shimmering
full-area skeleton continuously, from the lazy chunk load through
metadata fetch, token/SDK wait, and worker boot, until the real UI
mounts.

The skeleton is threaded down as an optional `loadingFallback` prop so
the shared `twenty-front-component-renderer` package stays
dependency-free (react-loading-skeleton stays in twenty-front). The
command-menu headless component opts out by not passing a fallback, so
it stays blank as before.

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packages/twenty-front/src/modules/page-layout/widgets/front-component/components/FrontComponentWidgetRenderer.tsx

@@ -3,6 +3,7 @@ import { Suspense, lazy } from 'react';
 
 import { isDefined } from 'twenty-shared/utils';
 
+import { FrontComponentSkeletonLoader } from '@/front-components/components/FrontComponentSkeletonLoader';
 import { usePageLayoutContentContext } from '@/page-layout/contexts/PageLayoutContentContext';
 import { useIsPageLayoutInEditMode } from '@/page-layout/hooks/useIsPageLayoutInEditMode';
 import { type PageLayoutWidget } from '@/page-layout/types/PageLayoutWidget';
@@ -57,10 +58,11 @@ export const FrontComponentWidgetRenderer = ({
       isCanvasLayout={layoutMode === PageLayoutTabLayoutMode.CANVAS}
       isInEditMode={isPageLayoutInEditMode}
     >
-      <Suspense fallback={null}>
+      <Suspense fallback={<FrontComponentSkeletonLoader />}>
         <FrontComponentRenderer
           frontComponentId={frontComponentId}
           selectedRecordIds={selectedRecordIds}
+          loadingFallback={<FrontComponentSkeletonLoader />}
         />
       </Suspense>
     </StyledContainer>