feat(board): Lightning-paid message board with LNbits and admin moderation

Add public /board flow: create invoice, webhook + confirm reconciliation, list
active messages, likes (Nostr), zap fallbacks. Admin table for hide/delete.

Include LNbits webhook body normalization (double-encoded JSON), POST
/api/messages/confirm/:hash, and root npm db:push script. Prisma models for
pending invoices and board messages.

Made-with: Cursor

frontend/components/admin/AdminSidebar.tsx

@@ -19,6 +19,7 @@ import {
   Inbox,
   ImageIcon,
   HelpCircle,
+  MessageSquare,
 } from "lucide-react";
 
 const navItems = [
@@ -28,6 +29,7 @@ const navItems = [
   { href: "/admin/blog", label: "Blog", icon: FileText, adminOnly: false },
   { href: "/admin/faq", label: "FAQ", icon: HelpCircle, adminOnly: false },
   { href: "/admin/submissions", label: "Submissions", icon: Inbox, adminOnly: false },
+  { href: "/admin/messages", label: "Board", icon: MessageSquare, adminOnly: false },
   { href: "/admin/moderation", label: "Moderation", icon: Shield, adminOnly: false },
   { href: "/admin/categories", label: "Categories", icon: Tag, adminOnly: false },
   { href: "/admin/users", label: "Users", icon: Users, adminOnly: true },