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/public/Navbar.tsx

@@ -14,6 +14,7 @@ const SECTION_LINKS = [{ label: "About", anchor: "about" }];
 
 const PAGE_LINKS = [
   { label: "Meetups", href: "/events" },
+  { label: "Board", href: "/board" },
   { label: "Community", href: "/community" },
   { label: "FAQ", href: "/faq" },
 ];