Rename Invoke button to Run Heartbeat for clarity

ui/src/pages/AgentDetail.tsx

@@ -468,7 +468,7 @@ export function AgentDetail() {
             disabled={agentAction.isPending || isPendingApproval}
           >
             <Play className="h-3.5 w-3.5 sm:mr-1" />
-            <span className="hidden sm:inline">Invoke</span>
+            <span className="hidden sm:inline">Run Heartbeat</span>
           </Button>
           {agent.status === "paused" ? (
             <Button