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/user-settings/package.json

@@ -66,6 +66,7 @@
     "@backstage/plugin-user-settings-common": "workspace:^",
     "@backstage/theme": "workspace:^",
     "@backstage/types": "workspace:^",
+    "@backstage/ui": "workspace:^",
     "@material-ui/core": "^4.12.2",
     "@material-ui/icons": "^4.9.1",
     "@material-ui/lab": "4.0.0-alpha.61",