The detail view could kill sessions, but the grid card's session rows were
enter-only. Add a ✕ kill button to each card session row (stopPropagation so it
doesn't also enter the session); makeSessionRow gains an optional onKill,
makeProjectCard an optional onKillSession, and mountProjects wires it to
DELETE /live-sessions/:id followed by a refresh.
Frontend-only. projects-panel tests +1 (51): ✕ present only with the callback,
click kills the right id without entering. Verified in-browser: a card with 2
sessions dropped to 1 after clicking ✕.
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