swarm-ui: the error and empty texts say agents and hives, not roster

The word named three different things. Only the four strings an operator reads change; code comments and names stay.

frontend/packages/swarm-ui/src/agent/detail/AgentDetailPopover.tsx

@@ -82,7 +82,7 @@ export function AgentDetailPopover({
           ) : row ? (
             <AgentDetail row={row} actions={actions} />
           ) : row === null ? (
-            <p>{agent} is not in the swarm's agent roster</p>
+            <p>{agent} is not in the swarm's agent list</p>
           ) : (
             <SkeletonLines label="the agent's details" count={4} />
           )}