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/config/auth.php

@@ -40,6 +40,11 @@ return [
             'driver' => 'session',
             'provider' => 'users',
         ],
+        
+        'api' => [
+            'driver' => 'api-key',
+            'provider' => 'gateway_users',
+        ],
     ],
 
     /*
@@ -69,6 +74,11 @@ return [
             'driver' => 'eloquent',
             'model' => env('AUTH_MODEL', App\Models\User::class),
         ],
+        
+        'gateway_users' => [
+            'driver' => 'eloquent',
+            'model' => App\Models\GatewayUser::class,
+        ],
 
         // 'users' => [
         //     'driver' => 'database',