Browsing into a smart (live-query) collection via /Items?ParentId={boxsetId}
returned 0 children while the BoxSet's ChildCount showed a non-zero count:
handleBoxSetChildren only read materialized library_collection_items via
ListItems, which is empty for smart collections whose membership is a query
evaluated at read time. Confirmed live — smart "Directed by ..." collections
returned TotalRecordCount 0 while materialized collections returned their items.
Branch handleBoxSetChildren on catalog.IsLiveQueryType: smart collections
resolve their members through the query executor (mirroring the web API's
loadLiveCollectionItems — Normalize/Validate/ApplySmartCollectionItemLimit,
library-scope intersection, access-filtered Preview), then feed the resulting
content IDs into the same hydration path as stored collections. A malformed or
invalid query definition degrades to an empty page (never a 500).
Hoist the duplicated intersectCollectionLibraryIDs helper into
catalog.IntersectCollectionLibraryIDs so the web and compat resolvers share one
implementation.
Adds smart_boxset_test.go (smart children resolve in query order, library-scope
intersection reaches the executor, malformed-query and no-executor degrade to
empty).
