add activity log with order timeline and global feed

Single activity_log table powering two views: chronological timeline
on each order detail page (replacing the old fulfilment card) and a
global feed at /admin/activity with tabs, category filters, search,
and pagination. Real-time via PubSub — new entries appear instantly,
nav badge updates across all admin pages.

Instrumented across all event points: Stripe webhooks, order notifier,
submission worker, fulfilment status worker, product sync worker, and
Oban exhausted-job telemetry. Contextual action buttons (retry
submission, retry sync, dismiss) with Oban unique constraints to
prevent double-enqueue. 90-day pruning via cron.

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

config/config.exs

@@ -99,7 +99,8 @@ config :berrypod, Oban,
        {"0 5 * * 1", Berrypod.Workers.RedirectPrunerWorker},
        {"30 3 * * *", Berrypod.Workers.DeadLinkCheckerWorker},
        {"0 2 * * *", Berrypod.Newsletter.CleanupWorker},
-       {"*/5 * * * *", Berrypod.Newsletter.ScheduledCampaignWorker}
+       {"*/5 * * * *", Berrypod.Newsletter.ScheduledCampaignWorker},
+       {"0 1 * * *", Berrypod.ActivityLog.PruneWorker}
      ]}
   ],
   queues: [images: 2, sync: 1, checkout: 1, newsletter: 1]