feat: user relay management, blog naddr sync, and OG image update

Add UserRelay API and dashboard relays tab with NIP-65 import, store post
naddr for Nostr articles, and ship Prisma migrations for board tables,
user relays, and post metadata.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/prisma/migrations/20260405073752_add_user_relay/migration.sql

@@ -0,0 +1,12 @@
+-- CreateTable
+CREATE TABLE "UserRelay" (
+    "id" TEXT NOT NULL PRIMARY KEY,
+    "pubkey" TEXT NOT NULL,
+    "url" TEXT NOT NULL,
+    "read" BOOLEAN NOT NULL DEFAULT true,
+    "write" BOOLEAN NOT NULL DEFAULT true,
+    "createdAt" DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "UserRelay_pubkey_url_key" ON "UserRelay"("pubkey", "url");