chore: 添加测试依赖配置和 gitignore

- 添加 frontend/package.json 包含 Vitest 测试依赖
- 添加 backend/.gitignore 排除 __pycache__, .coverage 等
- 添加 frontend/.gitignore 排除 node_modules, dist 等

测试运行验证:
- 后端: 268 tests skipped (TDD 红灯阶段)
- 前端: 95 tests skipped (TDD 红灯阶段)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/.gitignore

@@ -0,0 +1,13 @@
+__pycache__/
+*.py[cod]
+*$py.class
+.pytest_cache/
+.coverage
+htmlcov/
+.mypy_cache/
+*.egg-info/
+dist/
+build/
+.env
+.venv/
+venv/