feat: per-category email prefs, admin ops webhooks, per-user feature toggles (v0.61.0)

- Notification email preferences: every push category (follow, comment,
  reply, reaction, rating, mention, leftoverExpiring, shoppingList) now has
  an independent email toggle, plus a Weekly Digest toggle. Previously email
  sent unconditionally whenever the recipient had one; now gated the same
  way push already was. The weekly-digest cron route excludes opted-out
  users.

- Admin-only site-wide webhooks (Admin → Webhooks): new signups, support
  tickets, and reports filed can now fire an HMAC-signed HTTP webhook
  (Slack/Discord/ops alerting), independent of the existing per-user
  webhooks (which stay scoped to a user's own recipe/meal-plan/shopping-list
  events). Signing/delivery logic factored into lib/webhook-delivery.ts and
  shared by both dispatchers instead of duplicated.

- Settings → Features: users can hide Nutrition, Pantry, Meal Plan,
  Shopping Lists, Collections, or Messages from their own nav. Purely
  cosmetic — hidden pages stay reachable by direct link, nothing is
  access-restricted.

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

apps/web/lib/auth/server.ts

@@ -7,6 +7,7 @@ import { isSignupsDisabled } from "@/lib/site-settings";
 import { findValidInvite, consumeInvite, INVITE_COOKIE } from "@/lib/invites";
 import { generateUniqueUsername } from "@/lib/username";
 import { getRedis } from "@/lib/redis";
+import { dispatchAdminWebhook } from "@/lib/admin-webhooks";
 
 // Without this, better-auth's own rate limiter (sign-in/sign-up/2FA/password
 // reset throttles below) defaults to an in-process Map — fine for a single
@@ -178,6 +179,8 @@ export const auth = betterAuth({
             subject: "Welcome to Epicure",
             html: welcomeHtml(user.name),
           }).catch(() => {});
+
+          void dispatchAdminWebhook("user.signed_up", { id: user.id, email: user.email, name: user.name });
         },
       },
     },