Fix timezone issue: Set default timezone to Asia/Tokyo

- Update config/app.php to use APP_TIMEZONE from .env with Asia/Tokyo as default
- Add APP_TIMEZONE to .env.example
- Fixes issue where timestamps were displayed 9 hours behind (UTC vs JST)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/.env.example

@@ -7,6 +7,7 @@ APP_URL=http://localhost
 APP_LOCALE=en
 APP_FALLBACK_LOCALE=en
 APP_FAKER_LOCALE=en_US
+APP_TIMEZONE=Asia/Tokyo
 
 APP_MAINTENANCE_DRIVER=file
 # APP_MAINTENANCE_STORE=database

src/config/app.php

@@ -65,7 +65,7 @@
     |
     */
 
-    'timezone' => 'UTC',
+    'timezone' => env('APP_TIMEZONE', 'Asia/Tokyo'),
 
     /*
     |--------------------------------------------------------------------------