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

package.json

@@ -0,0 +1,9 @@
+{
+  "name": "belgian-bitcoin-embassy",
+  "private": true,
+  "scripts": {
+    "db:push": "npm run db:push --prefix backend",
+    "db:seed": "npm run db:seed --prefix backend",
+    "db:studio": "npm run db:studio --prefix backend"
+  }
+}