feat(admin): add admin panel with user management, daily puzzle CRUD, and activity graph

- Add admin page at /admin (restricted to ADMIN_EMAIL via proxy)
- Implement user ban/unban and deletion
- Add daily puzzle creation, modification, deletion
- Include 14-day activity chart with hover details
- Add User.banned field to schema and migrate database
- Block banned users from logging in
- Add ADMIN_EMAIL to .env.local configuration
- Update Prisma client after schema changes

package.json

@@ -12,8 +12,10 @@
     "postinstall": "npx node-gyp rebuild --directory node_modules/.pnpm/better-sqlite3@12.8.0/node_modules/better-sqlite3 2>/dev/null || true"
   },
   "dependencies": {
+    "@panva/hkdf": "^1.2.1",
     "@prisma/client": "^7.7.0",
     "bcryptjs": "^3.0.3",
+    "jose": "^6.2.2",
     "next": "16.2.3",
     "next-auth": "5.0.0-beta.30",
     "react": "19.2.4",