Replace heuristic-based most popular detection with Qobuz's actual
most_popular field from the catalog/search endpoint.
- Add CATALOG_SEARCH endpoint path
- Make app_id() and get_http() public on QobuzClient
- Add MostPopularItem enum with tagged serialization (artists/albums/tracks)
- Update search_all to use catalog/search and parse most_popular field
- Update SearchView template to use allResults.most_popular with new types
- Add MostPopularItem type to searchState store