Adds a "show activity" toggle to any running topology_run row on
the phase card. Expanded rows mount a compact SSE tail from
/api/topology-runs/{id}/events, rendering step/reasoning/tool
events as they arrive — same stream the LIVE tab consumes, just
scoped to one run.
Extracted the phase-runs list into PhaseRunsList to keep
MissionCanvas under the 1250-line budget.
