feat(certificates): admin certificate management UI

Admin can view, issue, and delete certificates. Student certificate
query now normalises the response shape (works with both paginated
and non-paginated API responses).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/services/api/admin-certificates.js

@@ -0,0 +1,10 @@
+import { http } from '@/services/api/http'
+import { buildUrl, endpoints } from '@/services/api/endpoints'
+
+export const apiGetAdminCertificates = (params) =>
+  http.get(endpoints.getAdminCertificates, { params })
+
+export const apiAddAdminCertificate = (payload) => http.post(endpoints.addAdminCertificate, payload)
+
+export const apiDeleteAdminCertificate = (id) =>
+  http.delete(buildUrl(endpoints.deleteAdminCertificate, { id }))