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

backend/prisma/schema.prisma

@@ -147,3 +147,27 @@ model Faq {
   createdAt      DateTime @default(now())
   updatedAt      DateTime @updatedAt
 }
+
+/// Pending Lightning invoice metadata (message is created only after payment via webhook).
+model BoardInvoicePending {
+  paymentHash String   @id
+  content     String
+  guestName   String?
+  pubkey      String?
+  profilePic  String?
+  createdAt   DateTime @default(now())
+}
+
+/// Paid board message (LNbits payment confirmed).
+model BoardMessage {
+  id          String   @id @default(uuid())
+  paymentHash String   @unique
+  content     String
+  authorName  String
+  pubkey      String?
+  profilePic  String?
+  satsPaid    Int
+  status      String   @default("active") // active, hidden, deleted
+  likeCount   Int      @default(0)
+  createdAt   DateTime @default(now())
+}