Add pipeline tag

Reorganize bundled assets into checkpoints/ and data/ folders

README: add Mosaic mosaic-tile header banner

README: reorder bottom sections; drop Field/Value header

README: move Citation to the very end

README: keep YAML frontmatter on HF; align body with GitHub

Add 'Getting the weights' note; align with GitHub mirror

Initial release: Mosaic weather model (era5 + hres variants)