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/GatewayUser.php

@@ -52,6 +52,11 @@ class GatewayUser extends Model implements Authenticatable
         return $this->hasMany(UsageLog::class, 'gateway_user_id', 'user_id');
     }
 
+    public function llmRequests()
+    {
+        return $this->hasMany(LlmRequest::class, 'gateway_user_id', 'user_id');
+    }
+
     // Scopes
     public function scopeActive($query)
     {