chore: [인프라] Slack 채널 분리 + logging 권한 + 문서 갱신

- Slack 알림 채널: product_infra → deploy_api
- logging.php daily/api 채널 permission 0664 추가
- CLAUDE.md, INDEX.md, 변경이력 문서 갱신

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),

config/services.php

@@ -43,7 +43,7 @@
     */
     'gemini' => [
         'api_key' => env('GEMINI_API_KEY'),
-        'model' => env('GEMINI_MODEL', 'gemini-2.0-flash'),
+        'model' => env('GEMINI_MODEL', 'gemini-2.5-flash'),
         'base_url' => env('GEMINI_BASE_URL', 'https://generativelanguage.googleapis.com/v1beta'),
     ],