feat: add SiteSettings model to manage forum and bug feature toggles

nest-backend/prisma/schema.prisma

@@ -221,6 +221,14 @@ model PollVote {
   @@id([userId, pollOptionId])
 }
 
+// ── Site Settings ──────────────────────────────────────────────────────────────
+
+model SiteSettings {
+  id           Int     @id @default(1)
+  forumEnabled Boolean @default(true)
+  bugsEnabled  Boolean @default(true)
+}
+
 // ── Team Members ───────────────────────────────────────────────────────────────
 
 model TeamMember {