feat(hunt): add public flag to hunts and implement hunt creation page

- Add 'public' boolean column to Hunt model with default true
- Update hunt admin UI to toggle 'public' flag
- Implement new hunt creation page with form supporting all hunt properties
- Add sidebar navigation item for hunt creation for authorized users
- Adjust home API to filter hunts by public flag only

prisma/schema.prisma

@@ -78,6 +78,7 @@ model Hunt {
   allowJoin     Boolean   @default(false)
   revealQuests  Boolean   @default(false)
   revealAnswers Boolean   @default(false)
+  public        Boolean   @default(true)
 
   creator   User @relation(fields: [creatorId], references: [id], onUpdate: Cascade, onDelete: Cascade)
   creatorId Int