docs updates for 2025-11-08 LTS

* `docs/cellxgene_census_docsite_landing.md`: add a banner announcement for new organisms * `docs/cellxgene_census_docsite_data_release_info.md`: * add section for the new build * call out the schema changes with pluralization of `disease` and non-unique `feature_name` * add commented scripts for producing the stats tables (it's more involved now with the additional organisms and pluralization) * adjust verbiage about release policy/cadence to be more realistic for 2026 * `api/python/notebooks/analysis_demo/comp_bio_census_info.ipynb`: rerun on new build and add a note about the `disease` pluralization * `api/python/notebooks/api_demo/census_duplicated_cells.ipynb`: fix a historical typo (human/mouse swap), rerun on new build and add a note about the `disease` pluralization