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/app/admin/layout.tsx

@@ -3,7 +3,7 @@ import { headers } from "next/headers";
 import { auth } from "@/lib/auth/server";
 import { db, users, eq } from "@epicure/db";
 import Link from "next/link";
-import { Shield, Users, BookOpen, Settings, BarChart3, ClipboardList, HardDrive, Bot, ArrowLeft, Gauge, Mail, Flag, History, LifeBuoy, TrendingUp } from "lucide-react";
+import { Shield, Users, BookOpen, Settings, BarChart3, ClipboardList, HardDrive, Bot, ArrowLeft, Gauge, Mail, Flag, History, LifeBuoy, TrendingUp, Webhook } from "lucide-react";
 import { cn } from "@/lib/utils";
 
 const adminNav = [
@@ -15,6 +15,7 @@ const adminNav = [
   { href: "/admin/reports", label: "Reports", icon: Flag },
   { href: "/admin/support", label: "Support", icon: LifeBuoy },
   { href: "/admin/tiers", label: "Tier Limits", icon: Gauge },
+  { href: "/admin/webhooks", label: "Webhooks", icon: Webhook },
   { href: "/admin/audit-logs", label: "Audit Logs", icon: ClipboardList },
   { href: "/admin/storage", label: "Storage", icon: HardDrive },
   { href: "/admin/ai-config", label: "AI Config", icon: Bot },