Override _post_view_url to return /post/show/{id} for the per-post
HTML scrape path. No _tag_api_url override — Moebooru has no batch
tag DAPI; the CategoryFetcher dispatch goes straight to per-post
HTML for these sites.
search() and get_post() now call prefetch_batch when a fetcher is
attached, same fire-and-forget pattern as gelbooru.py.