The selection bar's Set category opens the concept's simpleInput dialog
("Categorize selected images", one Category field, Cancel / Apply) and
posts the selection's distinct linked positive ids to
/prompt_manager/bulk/category. Images have no category of their own; the
listing's category filter matches the linked positive's, so that is what
changes. With no linked image checked nothing is posted and a toast says
so; on success the toast counts the prompts and any skipped images, then
the categories and the listing reload (clearing the selection); a failure
keeps the selection. The button ignores a second press while it runs.
The bulk category route now rejects anything but a non-empty list of at
most 1000 positive integer ids (deduplicated in order) and validates the
category with validate_category; bad JSON or a non-object body is a 400.
The response shape and the legacy admin request are unchanged.