dashboard: add 'All Workstreams' subtitle above filtered table

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

dashboard/src/workstreams.md

@@ -115,6 +115,8 @@ display(Plot.plot({
 }));
 ```
 
+## All Workstreams
+
 ```js
 display(_filtersForm);