Add environment variable example and update .gitignore

- Created a new .env.example file to provide a template for environment variables, including database connection details, JWT settings, encryption keys, and external API keys.
- Updated .gitignore to include additional test output directories and archive files, ensuring that unnecessary files are not tracked by Git.
- Removed outdated approval test reports and scripts that are no longer needed, streamlining the project structure.

These changes improve the clarity of environment configuration and maintain a cleaner repository.

backend-node/src/tests/env.setup.ts

@@ -6,8 +6,7 @@
 process.env.NODE_ENV = "test";
 // 실제 DB 연결을 위해 운영 데이터베이스 사용 (읽기 전용 테스트만 수행)
 process.env.DATABASE_URL =
-  process.env.TEST_DATABASE_URL ||
-  "postgresql://postgres:ph0909!!@39.117.244.52:11132/plm";
+  process.env.TEST_DATABASE_URL || "";
 process.env.JWT_SECRET = "test-jwt-secret-key-for-testing-only";
 process.env.PORT = "3001";
 process.env.DEBUG = "true"; // 테스트 시 디버그 로그 활성화