feat(engine): 添加核心基础设施 — engine/common 模块

- engine/__init__.py: 包入口，导出 Kline/KlineInterval/OrderBook/Ticker/Trade
- common/base.py: BaseStrategy 抽象基类，定义 on_kline/on_ticker/on_orderbook 回调
- common/models.py: Pydantic 数据模型，与 TS 侧 types 字段对齐，支持字段校验
- common/config.py: 全局配置加载（YAML），统一 engine/env.yaml 读取
- common/logger.py: 结构化日志，支持 JSON/pretty print 输出

engine/common/__init__.py

@@ -0,0 +1,23 @@
+# engine.common — 策略引擎公共模块
+
+from .models import Kline, KlineInterval, OrderBook, Ticker, Trade
+from .base import BaseStrategy, Signal, StrategyConfig
+from .logger import logger
+from .config import AppConfig, DBConfig, LoggingConfig, RedisConfig, config
+
+__all__ = [
+    "Kline",
+    "KlineInterval",
+    "OrderBook",
+    "Ticker",
+    "Trade",
+    "BaseStrategy",
+    "Signal",
+    "StrategyConfig",
+    "logger",
+    "config",
+    "AppConfig",
+    "DBConfig",
+    "RedisConfig",
+    "LoggingConfig",
+]