Fix STATIC_ROOT configuration and improve production settings

- Add STATIC_ROOT and MEDIA_ROOT settings with environment variable support
- Update settings.py to use environment variables for SECRET_KEY, DEBUG, ALLOWED_HOSTS, TIME_ZONE
- Improve docker-entrypoint.sh to auto-create static/media directories
- Always run collectstatic in Docker (not just production)
- Add check_settings.py script for configuration verification
- Add PRODUCTION_CHECKLIST.md for deployment guide
- Update .env.example with all configuration options
- Update .gitignore for proper static/media file handling

This fixes the ImproperlyConfigured error when deploying with Docker.

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

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

.env.example

@@ -1,7 +1,7 @@
-# Django 설정
-DJANGO_SECRET_KEY=your-secret-key-here
+# Django 기본 설정
+DJANGO_SECRET_KEY=your-secret-key-here-change-in-production
 DJANGO_DEBUG=False
-DJANGO_ALLOWED_HOSTS=localhost,127.0.0.1
+DJANGO_ALLOWED_HOSTS=localhost,127.0.0.1,yourdomain.com
 
 # 환경 설정
 DJANGO_ENV=production
@@ -9,9 +9,14 @@ DJANGO_ENV=production
 # 데이터베이스 (PostgreSQL 사용 시)
 # DATABASE_URL=postgresql://user:password@localhost:5432/dbname
 
-# 정적 파일
+# 정적 파일 (프로덕션)
 STATIC_ROOT=/app/staticfiles
 STATIC_URL=/static/
 
-# 타임존
+# 미디어 파일
+MEDIA_ROOT=/app/mediafiles
+MEDIA_URL=/media/
+
+# 국제화
 TIME_ZONE=Asia/Seoul
+LANGUAGE_CODE=en-us