feat: Phase 8 SaaS 확장 - 구독관리/결제내역 API 추가

- 사용량 조회 API (GET /subscriptions/usage)
- 데이터 내보내기 API (POST/GET /subscriptions/export)
- 결제 명세서 API (GET /payments/{id}/statement)
- DataExport 모델 및 마이그레이션 추가

database/migrations/2025_12_19_164035_create_data_exports_table.php

@@ -0,0 +1,41 @@
+<?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('data_exports', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('tenant_id')->constrained()->cascadeOnDelete()->comment('테넌트 ID');
+            $table->string('export_type', 50)->comment('내보내기 유형: all, users, products, orders, clients');
+            $table->string('status', 20)->default('pending')->comment('상태: pending, processing, completed, failed');
+            $table->string('file_path')->nullable()->comment('생성된 파일 경로');
+            $table->string('file_name')->nullable()->comment('다운로드 파일명');
+            $table->unsignedBigInteger('file_size')->nullable()->comment('파일 크기 (bytes)');
+            $table->json('options')->nullable()->comment('내보내기 옵션');
+            $table->timestamp('started_at')->nullable()->comment('처리 시작 시간');
+            $table->timestamp('completed_at')->nullable()->comment('처리 완료 시간');
+            $table->text('error_message')->nullable()->comment('에러 메시지');
+            $table->foreignId('created_by')->nullable()->constrained('users')->nullOnDelete()->comment('생성자');
+            $table->timestamps();
+
+            $table->index(['tenant_id', 'status']);
+            $table->index(['tenant_id', 'created_at']);
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('data_exports');
+    }
+};