- Change primary argument from TMDB size string (`w500`, `w1280`, etc.)
to category name (`posters`, `backdrops`, `stills`, `logos`,
`profiles`); optional size override remains as third argument
- Update all call sites across services, actions, pages, and route
handlers to use the new category-based API
- Update image.test.ts to match the new signature and replace
size-mapping test descriptions with category-name descriptions