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/api/admin.ts

@@ -225,6 +225,50 @@ export function triggerJob(jobName: string, options?: { target_model?: BacktestT
     .then((r) => r.data);
 }
 
+// System events (operational warnings / errors)
+export interface SystemEvent {
+  id: number;
+  severity: 'warning' | 'error' | string;
+  source: string;
+  code: string;
+  message: string;
+  symbol: string | null;
+  created_at: string | null;
+  acknowledged_at: string | null;
+}
+
+export interface SystemEventSummary {
+  days: number;
+  total: number;
+  unacknowledged: number;
+  unacknowledged_errors: number;
+  unacknowledged_warnings: number;
+}
+
+export function listSystemEvents(params?: {
+  days?: number;
+  severity?: string;
+  unacknowledged_only?: boolean;
+}) {
+  return apiClient
+    .get<SystemEvent[]>('admin/system-events', { params })
+    .then((r) => r.data);
+}
+
+export function getSystemEventSummary(days = 7) {
+  return apiClient
+    .get<SystemEventSummary>('admin/system-events/summary', { params: { days } })
+    .then((r) => r.data);
+}
+
+export function acknowledgeSystemEvents(days = 7) {
+  return apiClient
+    .post<{ acknowledged: number }>('admin/system-events/acknowledge', null, {
+      params: { days },
+    })
+    .then((r) => r.data);
+}
+
 // Data cleanup
 export function cleanupData(olderThanDays: number) {
   return apiClient