Add system alerts log with nav badge and Admin Alerts tab.

Persist job and ingestion warnings/errors for 7 days, surface a dismissible top-nav badge, treat stale OHLCV as a warning (e.g. ticker renames), and show market bar age on the ticker freshness chip.

frontend/src/pages/AdminPage.tsx

@@ -6,6 +6,7 @@ import { SentimentProviderSettings } from '../components/admin/SentimentProvider
 import { DataCleanup } from '../components/admin/DataCleanup';
 import { JobControls } from '../components/admin/JobControls';
 import { PipelineReadinessPanel } from '../components/admin/PipelineReadinessPanel';
+import { SystemEventsPanel } from '../components/admin/SystemEventsPanel';
 import { RecommendationSettings } from '../components/admin/RecommendationSettings';
 import { ScheduleSettings } from '../components/admin/ScheduleSettings';
 import { SettingsForm } from '../components/admin/SettingsForm';
@@ -15,7 +16,7 @@ import { UserTable } from '../components/admin/UserTable';
 import { PageHeader } from '../components/ui/PageHeader';
 import { Tabs } from '../components/ui/Tabs';
 
-const tabs = ['Users', 'Tickers', 'Settings', 'Jobs', 'Cleanup'] as const;
+const tabs = ['Users', 'Tickers', 'Settings', 'Jobs', 'Alerts', 'Cleanup'] as const;
 type Tab = (typeof tabs)[number];
 
 export default function AdminPage() {
@@ -49,6 +50,11 @@ export default function AdminPage() {
             <PipelineReadinessPanel />
           </div>
         )}
+        {activeTab === 'Alerts' && (
+          <div className="space-y-4">
+            <SystemEventsPanel />
+          </div>
+        )}
         {activeTab === 'Cleanup' && <DataCleanup />}
       </div>
     </div>