feat: auto-trigger scheduled agents + fix stale nextRun display

- Add background scheduler in entrypoint: calls /api/cron/agents every
  5 minutes to trigger due agents automatically
- Recalculate stale nextRun (past dates) in getAgents() so the display
  always shows a future time
- Agent card shows "En attente de déclenchement" instead of "il y a X"
  when nextRun is in the past

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

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

@@ -202,7 +202,9 @@ export function AgentCard({ agent, onEdit, onRefresh, onToggle }: AgentCardProps
             <Clock className="w-3 h-3" />
             {t('agents.schedule.nextRun')}{' '}
             {mounted
-              ? formatDistanceToNow(new Date(agent.nextRun), { addSuffix: true, locale: dateLocale })
+              ? new Date(agent.nextRun) > new Date()
+                ? formatDistanceToNow(new Date(agent.nextRun), { addSuffix: true, locale: dateLocale })
+                : t('agents.schedule.pending')
               : new Date(agent.nextRun).toISOString().split('T')[0]}
           </div>
         )}