feat:AI 토큰 사용량 추적 기능 추가

- ai_token_usages 테이블 마이그레이션 생성
- AiTokenUsage 모델 생성
- AiReportService에 usageMetadata 추출 및 저장 로직 추가

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Services/AiReportService.php

@@ -3,6 +3,7 @@
 namespace App\Services;
 
 use App\Models\Tenants\AiReport;
+use App\Models\Tenants\AiTokenUsage;
 use App\Models\Tenants\Card;
 use App\Models\Tenants\Deposit;
 use App\Models\Tenants\Purchase;
@@ -13,6 +14,7 @@
 use Illuminate\Pagination\LengthAwarePaginator;
 use Illuminate\Support\Facades\Http;
 use Illuminate\Support\Facades\Log;
+use Illuminate\Support\Str;
 
 class AiReportService extends Service
 {
@@ -361,6 +363,9 @@ private function callGeminiApi(array $inputData): array
             $result = $response->json();
             $text = $result['candidates'][0]['content']['parts'][0]['text'] ?? '';
 
+            // 토큰 사용량 저장
+            $this->saveTokenUsage($result, $model, 'AI리포트');
+
             // JSON 파싱
             $parsed = json_decode($text, true);
             if (json_last_error() !== JSON_ERROR_NONE) {
@@ -378,6 +383,46 @@ private function callGeminiApi(array $inputData): array
         }
     }
 
+    /**
+     * 토큰 사용량 저장
+     */
+    private function saveTokenUsage(array $apiResult, string $model, string $menuName): void
+    {
+        try {
+            $usage = $apiResult['usageMetadata'] ?? null;
+            if (! $usage) {
+                return;
+            }
+
+            $promptTokens = $usage['promptTokenCount'] ?? 0;
+            $completionTokens = $usage['candidatesTokenCount'] ?? 0;
+            $totalTokens = $usage['totalTokenCount'] ?? 0;
+
+            // Gemini 2.0 Flash 기준 단가 (USD per token)
+            $inputPricePerToken = 0.10 / 1_000_000;  // $0.10 / 1M tokens
+            $outputPricePerToken = 0.40 / 1_000_000;  // $0.40 / 1M tokens
+
+            $costUsd = ($promptTokens * $inputPricePerToken) + ($completionTokens * $outputPricePerToken);
+            $exchangeRate = (float) config('services.gemini.exchange_rate', 1400);
+            $costKrw = $costUsd * $exchangeRate;
+
+            AiTokenUsage::create([
+                'tenant_id' => $this->tenantId(),
+                'model' => $model,
+                'menu_name' => $menuName,
+                'prompt_tokens' => $promptTokens,
+                'completion_tokens' => $completionTokens,
+                'total_tokens' => $totalTokens,
+                'cost_usd' => $costUsd,
+                'cost_krw' => $costKrw,
+                'request_id' => Str::uuid()->toString(),
+                'created_by' => $this->apiUserId(),
+            ]);
+        } catch (\Exception $e) {
+            Log::warning('AI token usage save failed', ['error' => $e->getMessage()]);
+        }
+    }
+
     /**
      * AI 프롬프트 생성
      */