Repoint product hub URLs at the real /products/<product>/v9/ pages

The two hub gist HTML files were a stand-in while the V2 nav wiring was
unresolved. That's fixed upstream and the docs-content `hub-pages` branch
now serves the real hub markdown, so product pills should link to the
canonical URLs (`/products/elasticsearch/v9`, `/products/kibana/v9`)
instead of the gist previews.

The two visual-reference gists are no longer used by any code path. The
design handoff gist is still referenced in the PR and remains the
human-facing UX/technical write-up.

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

Author: florent-leborgne

config/products.yml

@@ -147,7 +147,7 @@ products:
   elasticsearch:
     display: 'Elasticsearch'
     versioning: 'stack'
-    hub: 'https://htmlpreview.github.io/?https://gist.github.com/florent-leborgne/b2ddb83d7b849980d1668aef600d0139/raw/elasticsearch-hub.html'
+    hub: 'products/elasticsearch/v9'
   elasticsearch-client:
     display: 'Elasticsearch Client'
     versioning: 'stack'
@@ -208,7 +208,7 @@ products:
   kibana:
     display: 'Kibana'
     versioning: 'stack'
-    hub: 'https://htmlpreview.github.io/?https://gist.github.com/florent-leborgne/c9075416b50ec111a09897b7be4462cc/raw/kibana-hub.html'
+    hub: 'products/kibana/v9'
   logstash:
     display: 'Logstash'
     versioning: 'stack'