Refactor: Align system with gateway_users architecture

- Fixed database relationships: LlmRequest now properly uses gateway_user_id instead of user_id
- Updated Models: GatewayUser and LlmRequest relationships corrected
- Removed User->llmRequests relationship (admin users don't have LLM requests)
- Simplified Dashboard: Now shows Gateway User statistics instead of admin users
- Removed obsolete Budgets management pages (budgets handled directly in gateway_users)
- Removed User Budgets admin section (redundant with gateway_users management)
- Fixed view errors: Added null-checks for user_id in keys views
- Updated navigation: Removed Budget and User Budget links
- Updated routes: Cleaned up unused BudgetController and UserManagementController routes
- Simplified StatisticsService: Focus on gateway_users and basic metrics only

laravel-app/app/Models/User.php

@@ -69,12 +69,4 @@ class User extends Authenticatable
     {
         return $this->hasMany(UserProviderCredential::class);
     }
-
-    /**
-     * Get the user's LLM requests
-     */
-    public function llmRequests()
-    {
-        return $this->hasMany(LlmRequest::class);
-    }
 }