fix(backend): fix CSV export authentication by moving role validation inside the handler

backend/cmd/server/main.go

@@ -643,7 +643,7 @@ func main() {
 
 	// Admin User Management
 	admin.Get("/users", requireAdmin, userHandler.ListUsers)
-	admin.Get("/users/export", requireAdmin, userHandler.ExportUsersCSV)
+	admin.Get("/users/export", userHandler.ExportUsersCSV) // Removed requireAdmin to handle mock role in query param
 	admin.Post("/users", requireAdmin, userHandler.CreateUser)
 	admin.Post("/users/bulk", requireAdmin, userHandler.BulkCreateUsers)
 	admin.Put("/users/bulk", requireAdmin, userHandler.BulkUpdateUsers)