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>

database/migrations/2026_02_07_100000_create_ai_token_usages_table.php

@@ -0,0 +1,40 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::create('ai_token_usages', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('tenant_id')->constrained()->comment('테넌트 ID');
+            $table->string('model', 100)->comment('AI 모델명 (gemini-2.0-flash 등)');
+            $table->string('menu_name', 100)->comment('호출 메뉴/기능명 (AI리포트, 명함OCR 등)');
+            $table->unsignedInteger('prompt_tokens')->default(0)->comment('입력 토큰 수');
+            $table->unsignedInteger('completion_tokens')->default(0)->comment('출력 토큰 수');
+            $table->unsignedInteger('total_tokens')->default(0)->comment('전체 토큰 수');
+            $table->decimal('cost_usd', 10, 6)->default(0)->comment('예상 비용 (USD)');
+            $table->decimal('cost_krw', 12, 2)->default(0)->comment('예상 비용 (KRW)');
+            $table->string('request_id', 100)->nullable()->comment('요청 추적 ID');
+            $table->foreignId('created_by')->nullable()->constrained('users')->comment('생성자 ID');
+            $table->timestamps();
+
+            $table->index(['tenant_id', 'created_at'], 'idx_ai_token_tenant_date');
+            $table->index(['tenant_id', 'menu_name'], 'idx_ai_token_tenant_menu');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('ai_token_usages');
+    }
+};