feat: upgrade next-auth to v5.0.0-beta.29 and refactor authentication middleware

- Updated next-auth dependency in package.json to version 5.0.0-beta.29.
- Refactored create-admin script to use a valid email format.
- Implemented authentication middleware for various API routes to enforce access control.
- Refactored API route handlers to improve readability and maintainability.
- Enhanced error handling in authentication error page.
- Added detailed tests for authentication flow, including protected routes and NextAuth endpoints.

package.json

@@ -20,7 +20,7 @@
     "date-fns": "^4.1.0",
     "leaflet": "^1.9.4",
     "next": "15.1.8",
-    "next-auth": "^4.24.11",
+    "next-auth": "^5.0.0-beta.29",
     "proj4": "^2.19.3",
     "proj4leaflet": "^1.0.2",
     "react": "^19.0.0",