cleanup: remove MariaDB dependencies and files

- Remove MariaDB helper, schema, and initialization script
- Remove mysql2 dependency from package.json
- Update reset-admin.js to use SQLite DatabaseHelper
- Simplify .env.example to remove MariaDB configuration
- Update start-service.sh to use SQLite initialization
- Clean up all MariaDB references across codebase

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

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

.env.example

@@ -1,10 +1,5 @@
 # 개발 환경 설정 예시
-# Windows 개발환경용 MariaDB/MySQL 연결 설정
-DB_HOST=localhost
-DB_PORT=3306
-DB_USER=root
-DB_PASSWORD=
-DB_NAME=jaryo
+# SQLite 데이터베이스 사용 (설정 불필요)
 
 # NAS 배포 환경
 NODE_ENV=development