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/app/(app)/settings/notifications/page.tsx

@@ -2,6 +2,7 @@ import type { Metadata } from "next";
 import { headers } from "next/headers";
 import { auth } from "@/lib/auth/server";
 import { PushSubscribeButton } from "@/components/pwa/push-subscribe-button";
+import { NotificationCategoriesForm } from "@/components/settings/notification-categories-form";
 import { getMessages } from "@/lib/i18n/server";
 
 export const metadata: Metadata = {};
@@ -21,6 +22,16 @@ export default async function NotificationsPage() {
         </div>
         <PushSubscribeButton />
       </section>
+
+      <section className="rounded-xl border p-6 space-y-4">
+        <div>
+          <h2 className="font-semibold text-lg">{m.settingsForm.notificationCategories.title}</h2>
+          <p className="text-sm text-muted-foreground mt-1">
+            {m.settingsForm.notificationCategories.description}
+          </p>
+        </div>
+        <NotificationCategoriesForm />
+      </section>
     </div>
   );
 }