add URL redirects with ETS-cached plug, broken URL tracking, and admin UI

Redirects context with redirect/broken_url schemas, chain flattening,
ETS cache for fast lookups in the request pipeline. BrokenUrlTracker
plug logs 404s. Auto-redirect on product slug change via upsert_product
hook. Admin redirects page with active/broken tabs, manual create form.
RedirectPrunerWorker cleans up old broken URLs. 1227 tests passing.

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

config/config.exs

@@ -95,7 +95,8 @@ config :berrypod, Oban,
        {"*/30 * * * *", Berrypod.Orders.FulfilmentStatusWorker},
        {"0 */6 * * *", Berrypod.Sync.ScheduledSyncWorker},
        {"0 3 * * *", Berrypod.Analytics.RetentionWorker},
-       {"0 4 * * *", Berrypod.Orders.AbandonedCartPruneWorker}
+       {"0 4 * * *", Berrypod.Orders.AbandonedCartPruneWorker},
+       {"0 5 * * 1", Berrypod.Workers.RedirectPrunerWorker}
      ]}
   ],
   queues: [images: 2, sync: 1, checkout: 1]