feat: granular per-category push notification settings

New Settings → Notifications section with a toggle per category (follow,
comment, reply, reaction, rating, mention, leftover-expiring, shared
shopping list) — previously it was all-or-nothing (browser permission only).

userNotificationPrefs (one row per user, defaults all-on so existing users
see no behavior change until they opt out of something). Gated the push
send in the three places that dispatch one: lib/notifications.ts (the 6
in-app notification types), the leftover-expiry cron, and shopping-list-notify
— in-app notification-center entries and email are unaffected, this only
gates the push itself, matching the literal ask.

Verified locally: GET/PUT round-trips correctly, disabling a category
and confirming the settings page renders all 8 toggles.

apps/web/messages/en.json

@@ -1068,6 +1068,18 @@
     }
   },
   "settingsForm": {
+    "notificationCategories": {
+      "title": "Notification categories",
+      "description": "Choose which push notifications you want to receive.",
+      "follow": "New followers",
+      "comment": "Comments on your recipes",
+      "reply": "Replies to your comments",
+      "reaction": "Reactions to your comments",
+      "rating": "Ratings on your recipes",
+      "mention": "Mentions in comments",
+      "leftoverExpiring": "Leftovers expiring soon",
+      "shoppingList": "Shared shopping list updates"
+    },
     "profile": "Profile",
     "changePhoto": "Change photo",
     "removePhoto": "Remove photo",