feat(certifications): admin cert-type pages + sidebar nav

/certifications (guarded by certifications.manage) lists cert types with
inline create/edit, archive/restore (is_active), and delete (refused
server-side once granted). Sidebar gets a Certifications link in the
Admin block next to Forms & waivers. Awarding to members is a separate
permission handled from the Members page (next phase).

app/(app)/certifications/page.tsx

@@ -0,0 +1,17 @@
+import { requireCertificationsManagerPage } from '@/lib/certifications-guard'
+import { CertificationsClient } from './certifications-client'
+
+export const dynamic = 'force-dynamic'
+
+export default async function CertificationsPage() {
+  const { supabase, member } = await requireCertificationsManagerPage()
+
+  const { data: certifications } = await supabase
+    .from('certifications')
+    .select('id, name, description, validity_months, is_active, created_at, updated_at')
+    .eq('space_id', member.space_id)
+    .order('is_active', { ascending: false })
+    .order('name', { ascending: true })
+
+  return <CertificationsClient initial={certifications ?? []} />
+}