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

server/api/admin/hunt/[huntId]/index.post.ts

@@ -21,8 +21,9 @@ export default defineEventHandler(async (event) => {
         description_de: z.string().min(1).max(1000).trim(),
         description_en: z.string().min(1).max(1000).trim(),
         virtual: z.boolean(),
-        start: z.iso.datetime(),
-        end: z.iso.datetime(),
+        public: z.boolean(),
+        start: z.iso.datetime().nullable(),
+        end: z.iso.datetime().nullable(),
         allowJoin: z.boolean(),
         revealQuests: z.boolean(),
         revealAnswers: z.boolean()