chore: python tooling and Claude Code project settings

- pinned runtime/dev deps (폐쇄망 반입용 버전 고정)
- .env.example, .gitignore
- .claude/settings.json: 시크릿/env 읽기 차단, FastAPI dev 명령 허용

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,8 @@
+.env
+__pycache__/
+*.pyc
+.venv/
+venv/
+.pytest_cache/
+.ruff_cache/
+audit-log.jsonl