Two permissive ~100-image sets for the Train tab: huggan/smithsonian_butterflies_subset
(CC0, the classic diffusers-docs training set, imported as a subject set with a trigger
prompt since its metadata columns are species names not captions) and m1guelpf/nouns
(CC0, captioned pixel-art avatars via the text column). Both cap at 100 images.
Cover caption precedence, thumbnail generation and .thumbs exclusion,
caption write/clear, image delete cleanup, path-traversal rejection on
names and filenames, and example import with a mocked datasets.load_dataset
(files plus sidecars written, idempotent second call, cap respected, load
failure mapped to 502).
