chore: 添加项目配置文件

- 添加 Python 项目配置 (pyproject.toml)
- 添加环境变量示例 (.env.example)
- 添加 Docker 忽略文件 (.dockerignore)
- 添加 TypeScript 配置 (tsconfig.json, tsconfig.node.json)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/.env.example

@@ -0,0 +1,24 @@
+# Application
+APP_NAME=YG-Dataset
+DEBUG=true
+HOST=0.0.0.0
+PORT=8000
+ALLOWED_ORIGINS=*
+
+# Database - Use SQLite for development, PostgreSQL for production
+DATABASE_URL=sqlite+aiosqlite:///./ygdataset.db
+DATABASE_URL_SYNC=sqlite:///./ygdataset.db
+
+# Security
+SECRET_KEY=your-secret-key-change-in-production
+
+# File Storage
+UPLOAD_DIR=./uploads
+MAX_FILE_SIZE=104857600
+
+# LLM Settings
+DEFAULT_MODEL_PROVIDER=openai
+DEFAULT_MODEL_NAME=gpt-4o-mini
+
+# Logging
+LOG_LEVEL=INFO