Telemetry Events (new)

[thanos]

Event	When
[:drone, :swarm, :start]	Swarm started
[:drone, :swarm, :stop]	Swarm stopped
[:drone, :swarm, :command, :start]	Coordinated op begins (takeoff, land, run, …)
[:drone, :swarm, :command, :stop]	Coordinated op ends successfully
[:drone, :swarm, :command, :error]	Coordinated op ends with partial/error
[:drone, :swarm, :emergency]	Swarm-wide emergency requested

Metadata includes swarm name (or nil) and members list. Per-drone events
continue to fire from each Vehicle.