feat(audit): admin audit log

Audit log
- Add audit_log table (migration + schema) with index on created_at.
- Add auditLog service (writeAudit, getClientIp) and record events for backups
  (create, restore, upload-restore, delete, auto-settings), admin actions
  (users, OIDC, invites, system update, demo baseline, bag tracking, packing
  template delete, addons), and auth (app settings, MFA enable/disable).
- Add GET /api/admin/audit-log with pagination; fix invite insert row id lookup.
- Add AuditLogPanel and Admin tab; adminApi.auditLog.
- Add admin.tabs.audit and admin.audit.* strings in all locale files.
Note: Rebase feature branches so new DB migrations stay after existing ones
  (e.g. file_links) when merging upstream.

client/src/api/client.ts

@@ -163,6 +163,8 @@ export const adminApi = {
   listInvites: () => apiClient.get('/admin/invites').then(r => r.data),
   createInvite: (data: { max_uses: number; expires_in_days?: number }) => apiClient.post('/admin/invites', data).then(r => r.data),
   deleteInvite: (id: number) => apiClient.delete(`/admin/invites/${id}`).then(r => r.data),
+  auditLog: (params?: { limit?: number; offset?: number }) =>
+    apiClient.get('/admin/audit-log', { params }).then(r => r.data),
 }
 
 export const addonsApi = {