chore: [API] logging, docs, seeder 등 부수 정리

- LOGICAL_RELATIONSHIPS.md 보완
- Legacy5130Calculator 수정
- logging.php 설정 추가
- KyungdongItemSeeder 수정
- docs/INDEX.md, changes 문서 경로 수정

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

config/logging.php

@@ -67,6 +67,7 @@
 
         'daily' => [
             'driver' => 'daily',
+            'permission' => 0664,
             'path' => storage_path('logs/laravel.log'),
             'level' => env('LOG_LEVEL', 'debug'),
             'days' => env('LOG_DAILY_DAYS', 14),
@@ -138,6 +139,7 @@
         */
         'api' => [
             'driver' => 'daily',
+            'permission' => 0664,
             'path' => storage_path('logs/api/api.log'),
             'level' => 'info',
             'days' => env('API_LOG_DAYS', 14),