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/Http/Controllers/GatewayUserController.php

@@ -14,8 +14,7 @@ class GatewayUserController extends Controller
      */
     public function index(Request $request)
     {
-        $query = GatewayUser::with('budget')
-            ->withCount(['apiKeys', 'usageLogs']);
+        $query = GatewayUser::withCount(['apiKeys', 'usageLogs']);
 
         // Search
         if ($request->filled('search')) {
@@ -87,7 +86,7 @@ class GatewayUserController extends Controller
      */
     public function show(string $userId)
     {
-        $user = GatewayUser::with(['apiKeys', 'budget'])
+        $user = GatewayUser::with(['apiKeys'])
             ->findOrFail($userId);
 
         // Get usage statistics for last 30 days