agents: connect explicit version refresh to the selected owner
An explicit agent_cli.list {check_latest:true} now refreshes versions through the selected machine's registry-only carrier. Ordinary reads stay cached. The adapter checks capability support and the returned owner, preserving admission and cancellation checks.
Validation: five Swift suites pass 20 methods plus parameter cases. The Rust inventory gate passes formatting, clippy, compilation and 81 tests, including a two-owner registry/watch journey with no CLI execution. The command exits 0; the fleet controller subsequently marks the job cancelled after a cache-cleanup timeout, with workspace reset confirmed.
Installation and sign-in observations remain cached and partial. Stacked on #21401.
Changelog
Added: Explicit version refresh for the selected machine's agent inventory.