Add regression tests for paginated album filtering and counts

The genre+search filter bug and the wrong result counts both lived in getPaginatedAlbums without any test noticing. Before the backend gets rewritten, pin the correct behaviour down so the new implementation has to match it.

Integration tests covering:

• genre filter alone returns only albums with that genre
• search alone filters by album and artist name
• genre + search together applies both (the case that was broken)
• totalCount matches the filtered result set in all three cases, not the full table
• pagination: furtherPages flag and page boundaries with a known fixture set