ITenantsProvider.ListAsync causes memory/performance bottlenecks with high tenant counts

Currently, the ITenantsProvider interface requires implementing ListAsync(), which returns Task>. While this works for small deployments, it does not scale for multi-tenant SaaS environments with hundreds or thousands of tenants.

ListAsync() loading all tenant configurations into memory.

Start by reading the ITenantsProvider interface and tracing its ListAsync() implementations and callers. Determine how tenant configurations are loaded and identify existing tests or benchmarks for tenant enumeration; done should mean high-tenant-count usage no longer creates the reported memory and performance bottleneck.

Written by the indexing model from the issue text.