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/resources/views/gateway-users/show.blade.php

@@ -164,7 +164,7 @@
                 <div class="flex justify-between items-center mb-4">
                     <h2 class="text-lg font-semibold text-gray-900">API Keys</h2>
                     {{-- TODO: Enable when API Keys Management is implemented --}}
-                    {{-- <a href="{{ route('api-keys.create', ['user_id' => $user->user_id]) }}" 
+                    {{-- <a href="{{ route('keys.create', ['user_id' => $user->user_id]) }}" 
                        class="text-sm text-indigo-600 hover:text-indigo-900">
                         + Create Key
                     </a> --}}