[Observability:Streams] Add page-level description to Streams landing page (#268468)

Closes https://github.com/elastic/streams-program/issues/1106

## Summary
This PR adds a page level description to the streams landing page along
with a link to streams documentation.

<img width="1512" height="982" alt="Screenshot 2026-05-08 at 10 44
00 AM"
src="https://github.com/user-attachments/assets/a4d0562e-9f2e-4f45-9dcf-5b80847577cf"
/>

Author: couvq

x-pack/platform/plugins/shared/streams_app/public/components/stream_list_view/index.tsx

@@ -11,6 +11,7 @@ import {
   EuiEmptyPrompt,
   EuiFlexGroup,
   EuiFlexItem,
+  EuiLink,
   EuiLoadingElastic,
   useEuiTheme,
 } from '@elastic/eui';
@@ -47,6 +48,7 @@ export function StreamListView() {
     },
     core,
   } = context;
+  const streamsDocsLink = core.docLinks.links.observability.logsStreams;
   const { onPageReady } = usePerformanceContext();
   const router = useStreamsAppRouter();
 
@@ -213,6 +215,19 @@ export function StreamListView() {
             )}
           </EuiFlexGroup>
         }
+        description={
+          <>
+            {i18n.translate('xpack.streams.streamsListView.pageHeaderDescription', {
+              defaultMessage:
+                'Manage how your data is ingested, structured, and retained across all your streams.',
+            })}{' '}
+            <EuiLink href={streamsDocsLink} target="_blank">
+              {i18n.translate('xpack.streams.streamsListView.pageHeaderDescriptionLearnMoreLink', {
+                defaultMessage: 'Learn more',
+              })}
+            </EuiLink>
+          </>
+        }
       />
       <StreamsAppPageTemplate.Body grow>
         {streamsListFetch.loading && streamsListFetch.value === undefined ? (