feat: offline save-for-later + background sync for mark-cooked (v0.65.0)

Adds a "Save offline" button on the recipe page that force-refetches
the current page so the service worker's cache picks up a fresh copy
right now, plus a small IndexedDB-backed list (lib/offline-db.ts) of
what's been saved. The /offline fallback page now reads that list and
renders it instead of being a dead end with just a "go back" link.

Also fixes the service worker's network-first fetch handler, which
never wrote successful responses into its cache -- meaning the
existing offline page's claim that "recently visited recipes are
available" was never actually true. It populates the cache on every
successful GET now.

Background sync: marking a batch-cook dish as cooked while offline
(the only existing mark-cooked call site in the app) now queues the
request in IndexedDB instead of just failing, and registers a
Background Sync (public/sw.js's "sync" listener replays the queue)
for Chromium; lib/offline-queue.ts's online-event fallback covers
Safari/Firefox, which never fire that event at all. Both replay paths
read/write the same IndexedDB store so either one drains it.

Also removes apps/web/public/manifest.json, a stale static manifest
that layout.tsx used to link to before the previous commit pointed it
at the real generated route (app/manifest.ts) -- it had gone
unnoticed and unused since.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/messages/en.json

@@ -146,6 +146,7 @@
     "batchCookMarkCooked": "Mark as cooked today",
     "batchCookMarkSuccess": "Marked as cooked",
     "batchCookMarkFailed": "Failed to mark as cooked",
+    "batchCookMarkQueuedOffline": "Saved offline — will sync when you're back online",
     "batchCookExpiresOn": "Cooked — good until {date}",
     "servings": "{count} servings",
     "prep": "{mins}m prep",