fix: refresh buttons use "now" as to-date for queries

Instead of calling refetch() with stale time params, the refresh
buttons now set a toOverride state to new Date().toISOString(). This
flows into the query key, triggering a fresh fetch with the current
time as the upper bound. Both useApplicationLogs and useAgentEvents
hooks accept an optional toOverride parameter.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/pages/AgentHealth/AgentHealth.tsx

@@ -223,8 +223,9 @@ function AgentPerformanceContent({ agent }: { agent: AgentInstance }) {
 export default function AgentHealth() {
   const { appId } = useParams();
   const { data: agents } = useAgents(undefined, appId);
-  const { data: events, refetch: refetchEvents } = useAgentEvents(appId);
   const [eventSortAsc, setEventSortAsc] = useState(false);
+  const [eventRefreshTo, setEventRefreshTo] = useState<string | undefined>();
+  const { data: events } = useAgentEvents(appId, undefined, 50, eventRefreshTo);
 
   const [selectedInstance, setSelectedInstance] = useState<AgentInstance | null>(null);
   const [panelOpen, setPanelOpen] = useState(false);
@@ -509,7 +510,7 @@ export default function AgentHealth() {
               <button className={styles.sortBtn} onClick={() => setEventSortAsc((v) => !v)} title={eventSortAsc ? 'Oldest first' : 'Newest first'}>
                 {eventSortAsc ? '\u2191' : '\u2193'}
               </button>
-              <button className={styles.refreshBtn} onClick={() => refetchEvents()} title="Refresh">
+              <button className={styles.refreshBtn} onClick={() => setEventRefreshTo(new Date().toISOString())} title="Refresh">
                 &#x21bb;
               </button>
             </div>