Add Background Jobs dashboard for admin users

New admin page at /admin/jobs showing:
- PyPI cache job status (pending, in-progress, completed, failed)
- Failed task list with error details
- Retry individual packages or retry all failed
- Auto-refresh every 5 seconds (toggleable)
- Placeholder for future NPM cache jobs

Accessible from admin dropdown menu as "Background Jobs".

frontend/src/api.ts

@@ -746,3 +746,43 @@ export async function testUpstreamSource(id: string): Promise<UpstreamSourceTest
   });
   return handleResponse<UpstreamSourceTestResult>(response);
 }
+
+// =============================================================================
+// PyPI Cache Jobs API
+// =============================================================================
+
+import {
+  PyPICacheStatus,
+  PyPICacheTask,
+  PyPICacheRetryResponse,
+} from './types';
+
+export async function getPyPICacheStatus(): Promise<PyPICacheStatus> {
+  const response = await fetch('/pypi/cache/status', {
+    credentials: 'include',
+  });
+  return handleResponse<PyPICacheStatus>(response);
+}
+
+export async function getPyPICacheFailedTasks(limit: number = 50): Promise<PyPICacheTask[]> {
+  const response = await fetch(`/pypi/cache/failed?limit=${limit}`, {
+    credentials: 'include',
+  });
+  return handleResponse<PyPICacheTask[]>(response);
+}
+
+export async function retryPyPICacheTask(packageName: string): Promise<PyPICacheRetryResponse> {
+  const response = await fetch(`/pypi/cache/retry/${encodeURIComponent(packageName)}`, {
+    method: 'POST',
+    credentials: 'include',
+  });
+  return handleResponse<PyPICacheRetryResponse>(response);
+}
+
+export async function retryAllPyPICacheTasks(): Promise<PyPICacheRetryResponse> {
+  const response = await fetch('/pypi/cache/retry-all', {
+    method: 'POST',
+    credentials: 'include',
+  });
+  return handleResponse<PyPICacheRetryResponse>(response);
+}