FA renders its species/character/artist/type system tags as tag-block
anchors with a data-tag-name carrying a single-letter prefix
(s_/c_/a_-u_/t_) and a sibling tag-invalid span instead of a /search/
link. The existing keyword pass skips them, so they were lost.
Adds a Submission.CategorizedTags field exposing the four buckets with
the prefix stripped, plus an examples/categorized_tags runnable demo.
