Dev.DiagnosticsHandler (BB.TUI v0.2.0)

Dev-only command that publishes one of each newly-surfaced diagnostic message so they appear in the Events panel:

• a BB.Safety.HardwareError on [:safety, :error] — the detail behind an error badge. This publishes the report directly and does not trip the safety state machine; production errors arrive via BB.Safety.report_error/3, which also forces a disarm.
• an estimator BB.Message.Estimator.Pose on [:estimator, :base_link].

Both subtrees are subscribed by BB.TUI.App but not modelled in dedicated state, so they flow through the event log's catch-all. Run this to confirm the surfacing end to end.

Goal shape: %{} (no arguments).