Add complete Laravel LLM Gateway implementation

Core Features:
- Multi-provider support (OpenAI, Anthropic, DeepSeek, Gemini, Mistral)
- Provider service architecture with abstract base class
- Dynamic model discovery from provider APIs
- Encrypted per-user provider credentials storage

Admin Interface:
- Complete admin panel with Livewire components
- User management with CRUD operations
- API key management with testing capabilities
- Budget system with limits and reset schedules
- Usage logs with filtering and CSV export
- Model pricing management with cost calculator
- Dashboard with Chart.js visualizations

Database Schema:
- MariaDB migrations for all tables
- User provider credentials (encrypted)
- LLM request logging
- Budget tracking and rate limiting
- Model pricing configuration

API Implementation:
- OpenAI-compatible endpoints
- Budget checking middleware
- Rate limit enforcement
- Request logging jobs
- Cost calculation service

Testing:
- Unit tests for all provider services
- Provider factory tests
- Cost calculator tests

Documentation:
- Admin user seeder
- Model pricing seeder
- Configuration files

laravel-app/app/Http/Controllers/Api/ChatCompletionController.php

@@ -0,0 +1,83 @@
+<?php
+
+namespace App\Http\Controllers\Api;
+
+use App\Http\Controllers\Controller;
+use App\Http\Requests\ChatCompletionRequest;
+use App\Services\LLM\GatewayService;
+use App\Exceptions\{ProviderException, InsufficientBudgetException, RateLimitExceededException};
+use Illuminate\Http\JsonResponse;
+use Illuminate\Support\Facades\Log;
+
+class ChatCompletionController extends Controller
+{
+    public function __construct(
+        private GatewayService $gatewayService
+    ) {}
+
+    /**
+     * Handle chat completion request
+     *
+     * @param ChatCompletionRequest $request
+     * @return JsonResponse
+     */
+    public function create(ChatCompletionRequest $request): JsonResponse
+    {
+        try {
+            $user = $request->user();
+            
+            $result = $this->gatewayService->chatCompletion(
+                user: $user,
+                provider: $request->input('provider'),
+                model: $request->input('model'),
+                messages: $request->input('messages'),
+                options: $request->only(['temperature', 'max_tokens', 'top_p', 'frequency_penalty', 'presence_penalty', 'stop']),
+                ipAddress: $request->ip(),
+                userAgent: $request->userAgent()
+            );
+            
+            return response()->json($result, 200);
+            
+        } catch (InsufficientBudgetException $e) {
+            return response()->json([
+                'success' => false,
+                'error' => 'budget_exceeded',
+                'message' => $e->getMessage(),
+            ], 402); // Payment Required
+            
+        } catch (RateLimitExceededException $e) {
+            return response()->json([
+                'success' => false,
+                'error' => 'rate_limit_exceeded',
+                'message' => $e->getMessage(),
+                'retry_after' => $e->getRetryAfter(),
+            ], 429);
+            
+        } catch (ProviderException $e) {
+            Log::error('Provider error in chat completion', [
+                'user_id' => $request->user()->id,
+                'provider' => $request->input('provider'),
+                'error' => $e->getMessage(),
+            ]);
+            
+            return response()->json([
+                'success' => false,
+                'error' => 'provider_error',
+                'message' => $e->getMessage(),
+            ], $e->getCode() ?: 500);
+            
+        } catch (\Exception $e) {
+            Log::error('Unexpected error in chat completion', [
+                'user_id' => $request->user()->id,
+                'error' => $e->getMessage(),
+                'trace' => $e->getTraceAsString(),
+            ]);
+            
+            return response()->json([
+                'success' => false,
+                'error' => 'internal_error',
+                'message' => 'An unexpected error occurred. Please try again.',
+            ], 500);
+        }
+    }
+}