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/auth/package.json

@@ -49,6 +49,7 @@
   "dependencies": {
     "@backstage/errors": "workspace:^",
     "@backstage/frontend-plugin-api": "workspace:^",
+    "@backstage/theme": "workspace:^",
     "@backstage/ui": "workspace:^",
     "@remixicon/react": "^4.6.0",
     "react-use": "^17.2.4"