Supplier topic/categories were derived from quote line items' material
category and topic. The catalog v2.7 refactor decoupled materials from
categories, so that derivation now yields nothing and every supplier lost
its topic/category — the suppliers dashboard rendered without names,
because it groups topic → category → supplier.
The backend already returns the supplier's own category
(category_id FK + nested category{id,slug,name}); adaptSupplier simply
never read it. Now it is the primary source, with quote-derived values and
the local registry still taking precedence when present.
Verified against the live stack: all 7 suppliers return their category
from /suppliers, and the suppliers page renders names again.