#21401 agents: refresh inventory versions without probing or updating

Agent inventory can now refresh latest versions without probing CLIs or scheduling updates. A separate Rust registry-only operation updates cached version evidence, preserves older evidence on source failure, and bounds network work. Its native carrier checks the selected machine before contacting acpmux.

Validation: the daemon workflow passes all nine raw and nine native refresh cases. Fleet gates pass formatting, clippy, compilation, 80 inventory tests and 60 protocol tests; served-method coverage retains an existing skip. Regression cases fail before the fix.

App wiring is in #21402. Stacked on #21398.

Changelog

Added: Registry-only version refresh for cached agent inventory.