"Hosted test sharding through native Once commands"

Create a hosted CI matrix with once query test-plan --shards and run each assignment with once test --shard-plan --shard-index. Once uses its existing native Tuist authentication and configuration, without launching the Tuist CLI.

Hosted assignments preserve portable batch and fixture boundaries, including on fresh workers. Each partition submits one immutable report with native target/suite/name identities, ordered case retries, and explicit attempt and revision counters. Empty assignments run nothing; missing evidence, failed processes, and cancellation cannot produce a successful partition report.

This requires a release containing the hosted commands. Once 0.71.0 supports portable plans only.