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/migrations/20260730211734_add_public_to_hunt/migration.sql

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE "public"."Hunt" ADD COLUMN     "public" BOOLEAN NOT NULL DEFAULT true;