Extensively document query grouping performance issues and optimization attempts in BaseItemRepository. Add guides on PostgreSQL UUID aggregation limitations, recommended indexes, increasing database timeouts, and monitoring query performance. Current code reverts to original (slow) implementation due to EF Core/Npgsql limitations, with detailed comments and references to new docs. Provides clear workarounds and upgrade path for future `.DistinctBy()` support.
wjones
623af06e46