Fix API controllers to use correct database column names

- Fix model_pricing table references (model_id -> model, display_name -> model)
- Fix price columns (output_price_per_1k -> output_price_per_million)
- Add price conversion (per_million / 1000 = per_1k) in all API responses
- Add whereNotNull('model') filters to exclude invalid entries
- Add getModelDisplayName() helper method to all controllers
- Fix AccountController to use gateway_users budget fields directly
- Remove Budget model dependencies from AccountController
- Add custom Scramble server URL configuration for API docs
- Create ScrambleServiceProvider to set correct /api prefix
- Add migration to rename user_id to gateway_user_id in llm_requests
- Add custom ApiGuard for gateway_users authentication
- Update all API controllers: AccountController, ModelController, PricingController, ProviderController

All API endpoints now working correctly:
- GET /api/account
- GET /api/models
- GET /api/pricing
- GET /api/providers/{provider}

laravel-app/app/Models/Budget.php

@@ -55,8 +55,6 @@ class Budget extends Model
         return 'Unlimited';
     }
 
-    public function gatewayUsers()
-    {
-        return $this->hasMany(GatewayUser::class, 'budget_id', 'budget_id');
-    }
+    // Note: gateway_users have their own budget system (monthly_budget_limit, current_month_spending)
+    // and are not linked to this budgets table
 }