fix: refresh agents on tab focus + hide stale nextRun + add cron logging

- Add visibilitychange listener: refreshes agent data immediately when
  user returns to the tab (more reliable than interval-only polling)
- Only show toast for actions created within last 5 minutes to avoid
  false positives on page reload
- Hide "Prochaine exécution" line entirely if nextRun is in the past
  instead of showing confusing "En attente de déclenchement"
- Add detailed logging to cron endpoint for debugging

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

memento-note/components/agents/agent-card.tsx

@@ -197,14 +197,12 @@ export function AgentCard({ agent, onEdit, onRefresh, onToggle }: AgentCardProps
           <span>{t('agents.metadata.executions', { count: agent._count.actions })}</span>
         </div>
 
-        {agent.frequency !== 'manual' && agent.nextRun && (
+        {agent.frequency !== 'manual' && agent.nextRun && new Date(agent.nextRun) > new Date() && (
           <div className="flex items-center gap-1.5 text-xs text-muted-foreground mb-3">
             <Clock className="w-3 h-3" />
             {t('agents.schedule.nextRun')}{' '}
             {mounted
-              ? new Date(agent.nextRun) > new Date()
-                ? formatDistanceToNow(new Date(agent.nextRun), { addSuffix: true, locale: dateLocale })
-                : t('agents.schedule.pending')
+              ? formatDistanceToNow(new Date(agent.nextRun), { addSuffix: true, locale: dateLocale })
               : new Date(agent.nextRun).toISOString().split('T')[0]}
           </div>
         )}