Fix pkgdown: add bundled data and missing topics to reference index

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bschilder

_pkgdown.yml

@@ -158,3 +158,9 @@ reference:
       - get_window_limits
       - import_ucsc_bigwigs
       - test_enrichment
+      - annotation_file_name
+  - title: Bundled data
+    contents:
+      - NOTT2019_bigwig_metadata
+      - xgr_example
+      - XGR_enrichment_bootstrap