Refactor code and add loading components in marketing apps

This commit alters the source of the cache module import used in [...slug]/page.tsx from 'next/cache' to 'react'. Import statements in blog/page.tsx and docs/layout.tsx have been restructured for clarity, keeping local imports separate. Added new loading.tsx files in both blog and docs directories that exports the GlobalLoader from '@kit/ui/global-loader'.

apps/web/app/(marketing)/docs/[...slug]/page.tsx

@@ -1,4 +1,5 @@
-import { unstable_cache as cache } from 'next/cache';
+import { cache } from 'react';
+
 import { notFound } from 'next/navigation';
 
 import { ContentRenderer, createCmsClient } from '@kit/cms';