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/Providers/AppServiceProvider.php

@@ -2,6 +2,12 @@
 
 namespace App\Providers;
 
+use App\Auth\ApiKeyGuard;
+use Dedoc\Scramble\Scramble;
+use Dedoc\Scramble\Support\Generator\OpenApi;
+use Dedoc\Scramble\Support\Generator\SecurityScheme;
+use Dedoc\Scramble\Support\Generator\Server;
+use Illuminate\Support\Facades\Auth;
 use Illuminate\Support\ServiceProvider;
 
 class AppServiceProvider extends ServiceProvider
@@ -19,6 +25,71 @@ class AppServiceProvider extends ServiceProvider
      */
     public function boot(): void
     {
-        //
+        // Register custom API-Key Guard for gateway_users authentication
+        Auth::extend('api-key', function ($app, $name, array $config) {
+            return new ApiKeyGuard(
+                Auth::createUserProvider($config['provider']),
+                $app['request']
+            );
+        });
+
+        // Configure Scramble API Documentation
+        Scramble::extendOpenApi(function (OpenApi $openApi) {
+            $openApi->secure(
+                SecurityScheme::http('bearer', 'API-Key')
+            );
+
+            // Add development server
+            $openApi->servers = [
+                new Server('http://localhost', 'Local Development'),
+            ];
+            
+            // Add comprehensive API description
+            $openApi->info->description = "
+# Laravel LLM Gateway API
+
+Multi-provider LLM Gateway supporting OpenAI, Anthropic, Google Gemini, DeepSeek, and Mistral AI.
+
+## Authentication
+
+All API requests require authentication via API key in the `Authorization` header:
+
+```
+Authorization: Bearer llmg_your_api_key_here
+```
+
+Gateway users receive API keys from the admin interface. Each key is linked to a specific gateway user 
+with their own budget limits, rate limits, and provider credentials.
+
+## Providers
+
+- **openai** - OpenAI models (GPT-4, GPT-3.5-turbo, etc.)
+- **anthropic** - Anthropic Claude models (Claude 4, Claude 3.5 Sonnet, etc.)
+- **google** - Google Gemini models (Gemini Pro, Gemini Flash, etc.)
+- **deepseek** - DeepSeek models (DeepSeek Chat, DeepSeek Coder)
+- **mistral** - Mistral AI models (Mistral Large, Mistral Medium, etc.)
+
+## Rate Limits
+
+Each gateway user has configurable rate limits (default: 60 requests/hour).
+Rate limit information is returned in error responses when exceeded.
+
+## Budgets
+
+Monthly budget limits are enforced per gateway user. Costs are calculated based on 
+token usage and provider-specific pricing.
+
+## Error Handling
+
+The API returns structured error responses:
+
+- **400**: Bad Request - Invalid parameters
+- **401**: Unauthorized - Invalid or missing API key
+- **402**: Payment Required - Budget exceeded
+- **403**: Forbidden - User blocked
+- **429**: Too Many Requests - Rate limit exceeded
+- **500**: Internal Server Error - Unexpected error
+";
+        });
     }
 }