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/GatewayUserCredential.php

@@ -0,0 +1,62 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Support\Facades\Crypt;
+
+class GatewayUserCredential extends Model
+{
+    protected $fillable = [
+        'gateway_user_id',
+        'provider',
+        'api_key',
+        'organization_id',
+        'is_active',
+        'last_used_at',
+        'last_tested_at',
+        'test_status',
+        'test_error',
+    ];
+
+    protected $hidden = ['api_key'];
+
+    protected $casts = [
+        'is_active' => 'boolean',
+        'last_used_at' => 'datetime',
+        'last_tested_at' => 'datetime',
+    ];
+
+
+    // Automatic encryption for API keys
+    public function setApiKeyAttribute($value): void
+    {
+        $this->attributes['api_key'] = Crypt::encryptString($value);
+    }
+
+    public function getApiKeyAttribute($value): string
+    {
+        return Crypt::decryptString($value);
+    }
+
+    // Relationships
+    public function gatewayUser()
+    {
+        return $this->belongsTo(GatewayUser::class, 'gateway_user_id', 'user_id');
+    }
+
+    // Helper methods
+    public function markAsUsed(): void
+    {
+        $this->update(['last_used_at' => now()]);
+    }
+
+    public function markAsTested(bool $success, ?string $error = null): void
+    {
+        $this->update([
+            'last_tested_at' => now(),
+            'test_status' => $success ? 'success' : 'failed',
+            'test_error' => $error,
+        ]);
+    }
+}