feat: 트리거 감사로그 operation_id 컬럼 추가 및 요청별 UUID 설정

- trigger_audit_logs 테이블에 operation_id(VARCHAR 36) 컬럼 추가
- ix_trig_operation 인덱스 생성 (일괄 롤백 조회용)
- SetAuditSessionVariables 미들웨어에서 요청마다 @sam_operation_id UUID 설정

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

app/Http/Middleware/SetAuditSessionVariables.php

@@ -5,12 +5,16 @@
 use Closure;
 use Illuminate\Http\Request;
 use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Str;
 use Symfony\Component\HttpFoundation\Response;
 
 class SetAuditSessionVariables
 {
     public function handle(Request $request, Closure $next): Response
     {
+        // 요청 단위 operation_id (인증 여부와 무관하게 항상 설정)
+        DB::statement('SET @sam_operation_id = ?', [Str::uuid()->toString()]);
+
         if (auth()->check()) {
             DB::statement('SET @sam_actor_id = ?', [auth()->id()]);
             DB::statement('SET @sam_session_info = ?', [