Migrate NFS pages to HeaderPage

Always render the plugin header for page blueprints and move page-level actions into the Backstage UI header pattern for affected NFS pages.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor

plugins/api-docs/package.json

@@ -62,6 +62,7 @@
     "@backstage/plugin-catalog-common": "workspace:^",
     "@backstage/plugin-catalog-react": "workspace:^",
     "@backstage/plugin-permission-react": "workspace:^",
+    "@backstage/ui": "workspace:^",
     "@graphiql/react": "0.29.0",
     "@material-ui/core": "^4.12.2",
     "@material-ui/icons": "^4.9.1",